diff --git a/sanguo_trader/engine.py b/sanguo_trader/engine.py
new file mode 100644
index 0000000..398a500
--- /dev/null
+++ b/sanguo_trader/engine.py
@@ -0,0 +1,112 @@
+"""PaperEngine 模拟盘主循环（逐根 bar 重放 + 双层记账 + 持久化，spec §4/§9）。
+
+run()：逐 bar → T+1 解冻 → 撮合上一根 next_open pending（用当前 bar）→ 喂策略
+on_bar 收新单 → current_close 当根撮合 / next_open 缓冲到下根 → 盯市 → 入库。
+raw 首版 fallback qfq（spec §17），信号与撮合共用一套（标注）。
+"""
+import logging
+
+import pandas as pd
+
+from .account import Account
+from .matcher import cross_order
+from .models import MatchSession, PaperTrade
+from .persistence import save_daily_balance, save_trade, update_checkpoint
+from .strategy_runner import StrategyRunner
+
+logger = logging.getLogger(__name__)
+
+
+def _to_series(bar) -> pd.Series:
+    return pd.Series({
+        "open": bar.open_price, "high": bar.high_price,
+        "low": bar.low_price, "close": bar.close_price,
+        "date": getattr(bar, "datetime", ""),
+    })
+
+
+def _trade_to_dict(t: PaperTrade, bar_date) -> dict:
+    return {
+        "strategy_id": t.strategy_id, "symbol": t.symbol,
+        "direction": t.side.value, "price": t.price, "volume": t.volume,
+        "commission": t.commission, "stamp_duty": t.stamp_duty,
+        "transfer_fee": t.transfer_fee,
+        "bar_date": str(bar_date), "match_session": t.match_session.value,
+    }
+
+
+class PaperEngine:
+    def __init__(self, account: Account, runners: list[StrategyRunner],
+                 data_source, cfg, db_path: str, account_id: int,
+                 symbols: list[str], start: str, end: str,
+                 interval: str = "d") -> None:
+        self.account = account
+        self.runners = runners
+        self.data_source = data_source
+        self.cfg = cfg
+        self.db_path = db_path
+        self.account_id = account_id
+        self.symbols = symbols
+        self.start = start
+        self.end = end
+        self.interval = interval
+
+    def run(self) -> None:
+        prev_close: dict[str, float] = {}
+        pending: list = []   # [(order, runner)] next_open 待下根撮合
+        bar_count = 0
+        for bar_date, bars in self.data_source.iter_bars(
+            self.symbols, self.start, self.end, self.interval, "qfq", None
+        ):
+            bar_count += 1
+            self.account.unfreeze_all()
+            for r in self.runners:
+                r.unfreeze_all()
+            # 1. 撮合上一根 pending（next_open，用当前 bar）
+            if pending:
+                for order, runner in pending:
+                    self._match(order, runner, bars, prev_close, bar_date)
+                pending = []
+            # 2. 喂策略 on_bar → 收新单
+            for runner in self.runners:
+                sym = runner.symbol
+                if sym and sym in bars:
+                    runner.paper_cta_engine.on_bar(bars[sym])
+                    for order in runner.paper_cta_engine.pop_orders():
+                        if order.match_session == MatchSession.NEXT_OPEN:
+                            pending.append((order, runner))
+                        else:   # current_close 当根撮合
+                            self._match(order, runner, bars, prev_close, bar_date)
+            # 3. 盯市 + 入库
+            closes = {s: bars[s].close_price for s in bars}
+            self.account.mark_to_market(closes)
+            save_daily_balance(
+                self.db_path, self.account_id, str(bar_date),
+                self.account.cash, self.account.market_value, self.account.equity,
+                is_checkpoint=(bar_count % 500 == 0),
+            )
+            update_checkpoint(self.db_path, self.account_id, str(bar_date))
+            prev_close = closes
+
+    def _match(self, order, runner, bars, prev_close, bar_date) -> None:
+        if order.symbol not in bars:
+            return
+        match_bar = _to_series(bars[order.symbol])
+        pc = prev_close.get(order.symbol, order.price)
+        result = cross_order(order, match_bar, pc, self.cfg)
+        if isinstance(result, PaperTrade):
+            if self.account.cash_enough(result):
+                self.account.apply_trade(result)
+                runner.apply_trade(result)
+                save_trade(self.db_path, self.account_id,
+                           _trade_to_dict(result, bar_date))
+            else:
+                save_trade(self.db_path, self.account_id,
+                           {"strategy_id": order.strategy_id, "symbol": order.symbol,
+                            "bar_date": str(bar_date)},
+                           rejected=True, reject_reason="insufficient_cash")
+        else:   # PaperReject
+            save_trade(self.db_path, self.account_id,
+                       {"strategy_id": order.strategy_id, "symbol": order.symbol,
+                        "bar_date": str(bar_date)},
+                       rejected=True, reject_reason=result.reason)
diff --git a/sanguo_trader/strategy_runner.py b/sanguo_trader/strategy_runner.py
index a111aab..906c6ad 100644
--- a/sanguo_trader/strategy_runner.py
+++ b/sanguo_trader/strategy_runner.py
@@ -7,10 +7,12 @@ from .position_ledger import PositionLedger
 
 
 class StrategyRunner:
-    def __init__(self, strategy_id: str, strategy=None, paper_cta_engine=None) -> None:
+    def __init__(self, strategy_id: str, strategy=None, paper_cta_engine=None,
+                 symbol: str = "") -> None:
         self.strategy_id: str = strategy_id
         self.strategy = strategy
         self.paper_cta_engine = paper_cta_engine
+        self.symbol: str = symbol
         self.positions: dict[str, PositionLedger] = {}
         self.realized_pnl: float = 0.0
         self.commission_paid: float = 0.0
diff --git a/tests/trader/test_engine.py b/tests/trader/test_engine.py
new file mode 100644
index 0000000..b6e168a
--- /dev/null
+++ b/tests/trader/test_engine.py
@@ -0,0 +1,93 @@
+"""PaperEngine 主循环测试（mock data_source + mock 策略，spec §4）。"""
+from types import SimpleNamespace
+
+from sanguo_trader.account import Account
+from sanguo_trader.cta_adapter import PaperCtaEngine
+from sanguo_trader.engine import PaperEngine
+from sanguo_trader.models import AccountConfig, MatchSession
+from sanguo_trader.persistence import (
+    init_db, list_daily_balance, list_trades, save_account,
+)
+from sanguo_trader.strategy_runner import StrategyRunner
+
+
+def _bar(date, o, h, l, c):
+    return SimpleNamespace(open_price=o, high_price=h, low_price=l,
+                           close_price=c, datetime=date)
+
+
+class _FakeDataSource:
+    def __init__(self, sections):
+        self.sections = sections
+
+    def iter_bars(self, symbols, start, end, interval, adjust="qfq", cfg=None):
+        del symbols, start, end, interval, adjust, cfg
+        for date, bars in self.sections:
+            yield date, bars
+
+
+class _AlwaysBuyStrategy:
+    def __init__(self, engine, vt_symbol):
+        self.cta_engine = engine
+        self.vt_symbol = vt_symbol
+
+    def on_bar(self, bar):
+        self.cta_engine.send_order(self, "LONG", "OPEN", bar.close_price, 100)
+
+
+def _build(tmp_path, sections, match_session=MatchSession.NEXT_OPEN):
+    db = str(tmp_path / "e.db")
+    init_db(db)
+    aid = save_account(db, {"name": "t", "initial_capital": 1_000_000})
+    cfg = AccountConfig(initial_capital=1_000_000)
+    account = Account(1_000_000)
+    cta = PaperCtaEngine("s1", match_session=match_session)
+    strat = _AlwaysBuyStrategy(cta, "600000.SSE")
+    cta.set_strategy(strat)
+    runner = StrategyRunner("s1", strategy=strat, paper_cta_engine=cta, symbol="600000")
+    pe = PaperEngine(account, [runner], _FakeDataSource(sections), cfg, db, aid,
+                     symbols=["600000"], start="2024-01-01", end="2024-12-31")
+    return pe, db, aid, account, runner
+
+
+def test_engine_next_open_fills_at_next_bar_open(tmp_path):
+    sections = [
+        ("2024-01-01", {"600000": _bar("2024-01-01", 10.0, 10.5, 9.5, 10.0)}),
+        ("2024-01-02", {"600000": _bar("2024-01-02", 10.5, 11.0, 10.0, 10.8)}),
+        ("2024-01-03", {"600000": _bar("2024-01-03", 10.8, 11.5, 10.5, 11.0)}),
+    ]
+    pe, db, aid, *_ = _build(tmp_path, sections)
+    pe.run()
+    fills = [t for t in list_trades(db, aid) if not t["rejected"]]
+    # day1 信号→day2 撮合@10.5(open)；day2 信号→day3 撮合@10.8(open)；day3 信号无day4
+    assert len(fills) == 2
+    assert fills[0]["price"] == 10.5
+    assert fills[1]["price"] == 10.8
+
+
+def test_engine_current_close_fills_same_bar(tmp_path):
+    sections = [
+        ("2024-01-01", {"600000": _bar("2024-01-01", 10.0, 10.5, 9.5, 10.0)}),
+        ("2024-01-02", {"600000": _bar("2024-01-02", 10.5, 11.0, 10.0, 10.8)}),
+    ]
+    pe, db, aid, *_ = _build(tmp_path, sections, match_session=MatchSession.CURRENT_CLOSE)
+    pe.run()
+    fills = [t for t in list_trades(db, aid) if not t["rejected"]]
+    assert len(fills) == 2
+    assert fills[0]["price"] == 10.0   # 当根 close
+    assert fills[1]["price"] == 10.8
+
+
+def test_engine_daily_balance_and_consistency(tmp_path):
+    sections = [
+        ("2024-01-01", {"600000": _bar("2024-01-01", 10.0, 10.5, 9.5, 10.0)}),
+        ("2024-01-02", {"600000": _bar("2024-01-02", 10.5, 11.0, 10.0, 10.8)}),
+        ("2024-01-03", {"600000": _bar("2024-01-03", 10.8, 11.5, 10.5, 11.0)}),
+    ]
+    pe, db, aid, account, runner = _build(tmp_path, sections)
+    pe.run()
+    balances = list_daily_balance(db, aid)
+    assert len(balances) == 3
+    # 总账持仓 = 分户持仓（day2+day3 各买100 = 200）
+    assert account.positions["600000"].volume == 200
+    assert runner.positions["600000"].volume == 200