diff --git a/AssetManager.Services/PortfolioNavService.cs b/AssetManager.Services/PortfolioNavService.cs
index 94b0682..ad010b6 100644
--- a/AssetManager.Services/PortfolioNavService.cs
+++ b/AssetManager.Services/PortfolioNavService.cs
@@ -394,6 +394,14 @@ public class PortfolioNavService : IPortfolioNavService
                     if (holdings.ContainsKey(tx.StockCode))
                     {
                         var existing = holdings[tx.StockCode];
+                        
+                        // 安全检查：防止除零
+                        if (existing.shares <= 0)
+                        {
+                            holdings.Remove(tx.StockCode);
+                            continue;
+                        }
+                        
                         decimal soldRatio = tx.Amount / existing.shares;
                         decimal remainingShares = existing.shares - tx.Amount;
                         decimal remainingCost = existing.cost * (1 - (decimal)soldRatio);
@@ -407,8 +415,11 @@ public class PortfolioNavService : IPortfolioNavService
                             holdings[tx.StockCode] = (remainingShares, remainingCost, existing.currency, existing.assetType);
                         }
 
-                        // 按比例减少累计投入成本（关键修复：不再用卖出金额）
-                        decimal costToReduce = cumulativeCost * (decimal)soldRatio;
+                        // 按比例减少累计投入成本（修复：使用该标的的成本，而非全局累计成本）
+                        // 先将该标的的成本转换为目标币种
+                        decimal existingCostInTarget = await _exchangeRateService.ConvertAmountAsync(
+                            existing.cost, existing.currency ?? targetCurrency, targetCurrency);
+                        decimal costToReduce = existingCostInTarget * (decimal)soldRatio;
                         cumulativeCost -= costToReduce;
                     }
                 }