diff --git a/emis-biz/src/main/java/com/xdadan/erp/emis/service/impl/EmisSettleBillServiceImpl.java b/emis-biz/src/main/java/com/xdadan/erp/emis/service/impl/EmisSettleBillServiceImpl.java
index b9d4e09bf..c5cf4adbd 100644
--- a/emis-biz/src/main/java/com/xdadan/erp/emis/service/impl/EmisSettleBillServiceImpl.java
+++ b/emis-biz/src/main/java/com/xdadan/erp/emis/service/impl/EmisSettleBillServiceImpl.java
@@ -394,8 +394,21 @@ public class EmisSettleBillServiceImpl extends EmisBaseService implements IEmisS
                 }
                 else{
                     Date billMonthDate = DateUtils.parseDate(emisSettleBill.getBillMonth() + "-"+settleDay);
-                    paymentDueDate = DateUtils.addMonths(billMonthDate,1);
-                    paymentDueDate= DateUtils.addDays(paymentDueDate,creditPeriod.intValue());
+
+                    // credit_period 为 30/60/90 且结算日为每月 1 号时，按对应月份月末作为最后付款日
+                    if ((creditPeriod.intValue() == 30 || creditPeriod.intValue() == 60 || creditPeriod.intValue() == 90)
+                            && monthUser.getSettleDay() == 1) {
+                        Calendar cal = Calendar.getInstance();
+                        cal.setTime(billMonthDate);
+                        // 30 -> 加 1 个月，60 -> 加 2 个月，90 -> 加 3 个月
+                        cal.add(Calendar.MONTH, creditPeriod.intValue() / 30);
+                        // 设置为该月的最后一天
+                        cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH));
+                        paymentDueDate = cal.getTime();
+                    } else {
+                        paymentDueDate = DateUtils.addMonths(billMonthDate,1);
+                        paymentDueDate= DateUtils.addDays(paymentDueDate,creditPeriod.intValue());
+                    }
                 }
 
                 // 最后付款时间
@@ -441,10 +454,21 @@ public class EmisSettleBillServiceImpl extends EmisBaseService implements IEmisS
                     updBill.setCreditPeriod(creditPeriod);
                     updBill.setSettleDay(settleDay);
 
-                    // 现金账期从寄件开始10天
+                    // 根据账期与结算日计算最后付款时间
                     Date billMonthDate = DateUtils.parseDate(oldEmisSettleBill.getBillMonth() + "-" + settleDay);
-                    Date paymentDueDate = DateUtils.addMonths(billMonthDate, 1);
-                    paymentDueDate = DateUtils.addDays(paymentDueDate, creditPeriod.intValue());
+                    Date paymentDueDate;
+
+                    if ((creditPeriod.intValue() == 30 || creditPeriod.intValue() == 60 || creditPeriod.intValue() == 90)
+                            && settleDay == 1) {
+                        Calendar cal = Calendar.getInstance();
+                        cal.setTime(billMonthDate);
+                        cal.add(Calendar.MONTH, creditPeriod.intValue() / 30);
+                        cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH));
+                        paymentDueDate = cal.getTime();
+                    } else {
+                        paymentDueDate = DateUtils.addMonths(billMonthDate, 1);
+                        paymentDueDate = DateUtils.addDays(paymentDueDate, creditPeriod.intValue());
+                    }
 
                     // 最后付款时间
                     updBill.setPaymentDueDate(paymentDueDate);