diff --git a/docs/ENVIRONMENT_VARIABLES.md b/docs/ENVIRONMENT_VARIABLES.md
index ded703e..d35b88d 100644
--- a/docs/ENVIRONMENT_VARIABLES.md
+++ b/docs/ENVIRONMENT_VARIABLES.md
@@ -193,12 +193,21 @@ FAL_API_KEY="fal-1234567890abcdefghijklmnopqrstuvwxyz"
 | `NEXTAUTH_URL` | NextAuth URL (same as app URL) | `https://prmbr.com` |
 | `NEXTAUTH_SECRET` | NextAuth secret for JWT signing | Random 32-character string |
 
+### Optional Variables
+
+| Variable | Description | Default | Example |
+|----------|-------------|---------|---------|
+| `FEE_CALCULATION_MULTIPLIER` | Fee calculation multiplier for AI model costs | `10.0` | `5.0` |
+
 ### Configuration
 ```bash
 # Application Settings
 NEXT_PUBLIC_APP_URL="https://prmbr.com"
 NEXTAUTH_URL="https://prmbr.com"
 NEXTAUTH_SECRET="your-super-secret-nextauth-secret-32chars"
+
+# Fee Calculation (Optional - defaults to 10x)
+FEE_CALCULATION_MULTIPLIER="10.0"
 ```
 
 ### Generating NEXTAUTH_SECRET
@@ -269,6 +278,9 @@ FAL_API_KEY="fal-1234567890abcdefghijklmnopqrstuvwxyzABCDEF"
 NEXT_PUBLIC_APP_URL="http://localhost:3000"
 NEXTAUTH_URL="http://localhost:3000"
 NEXTAUTH_SECRET="super-secret-nextauth-development-key-32-chars-long"
+
+# Fee Calculation (Optional - defaults to 10x)
+FEE_CALCULATION_MULTIPLIER="10.0"
 ```
 
 ### 🌐 Full Production Configuration
@@ -311,6 +323,9 @@ FAL_API_KEY="fal-production-1234567890abcdefghijklmnopqrstuvwxyz"
 NEXT_PUBLIC_APP_URL="https://prmbr.com"
 NEXTAUTH_URL="https://prmbr.com"
 NEXTAUTH_SECRET="super-secret-production-nextauth-key-32-chars-long-secure"
+
+# Fee Calculation (Optional - defaults to 10x)
+FEE_CALCULATION_MULTIPLIER="10.0"
 ```
 
 ## 🔒 Security Best Practices
diff --git a/src/app/api/users/sync/route.ts b/src/app/api/users/sync/route.ts
index 25995e3..ef5ae65 100644
--- a/src/app/api/users/sync/route.ts
+++ b/src/app/api/users/sync/route.ts
@@ -67,14 +67,14 @@ export async function POST() {
     }
 
     if (isNewUser) {
-      // 为新用户添加系统赠送的5USD信用额度（1个月后过期）
+      // 为新用户添加系统赠送的2USD信用额度（1个月后过期）
       const expiresAt = new Date()
       expiresAt.setMonth(expiresAt.getMonth() + 1)
       
       try {
         await addCredit(
           user.id,
-          5.0,
+          2.0,
           'system_gift',
           '系统赠送 - 新用户礼包',
           expiresAt
diff --git a/src/lib/simulator-utils.ts b/src/lib/simulator-utils.ts
index 4c7df90..e7e633b 100644
--- a/src/lib/simulator-utils.ts
+++ b/src/lib/simulator-utils.ts
@@ -53,7 +53,7 @@ export function calculateCost(
     inputCostPer1k?: number | null
     outputCostPer1k?: number | null
   },
-  costMultiplier: number = 1.0
+  costMultiplier?: number
 ): number {
   const inputCostPer1k = model.inputCostPer1k || 0
   const outputCostPer1k = model.outputCostPer1k || 0
@@ -63,8 +63,12 @@ export function calculateCost(
   const outputCost = (outputTokens / 1000) * outputCostPer1k
   const baseCost = inputCost + outputCost
   
-  // 应用套餐费用倍率
-  return baseCost * costMultiplier
+  // 获取环境变量中的费用倍率，默认为 10 倍
+  const defaultMultiplier = parseFloat(process.env.FEE_CALCULATION_MULTIPLIER || '10.0')
+  const finalMultiplier = costMultiplier ?? defaultMultiplier
+  
+  // 应用费用倍率
+  return baseCost * finalMultiplier
 }
 
 /**