diff --git a/openhis-server-new/openhis-application/src/main/java/com/openhis/web/outpatient/mapper/CatalogMapper.java b/openhis-server-new/openhis-application/src/main/java/com/openhis/web/outpatient/mapper/CatalogMapper.java
new file mode 100644
index 000000000..423d59ed0
--- /dev/null
+++ b/openhis-server-new/openhis-application/src/main/java/com/openhis/web/outpatient/mapper/CatalogMapper.java
@@ -0,0 +1,23 @@
+package com.openhis.web.outpatient.mapper;
+
+import org.apache.ibatis.annotations.Mapper;
+import org.apache.ibatis.annotations.Param;
+import org.apache.ibatis.annotations.Select;
+
+/**
+ * 诊疗目录（Catalog）相关数据库操作 Mapper
+ *
+ * 该 Mapper 仅提供获取默认计量单位的查询，用于医嘱录入时的单位兜底。
+ */
+@Mapper
+public interface CatalogMapper {
+
+    /**
+     * 根据诊疗目录 ID 查询其默认的计量单位（total_unit）。
+     *
+     * @param catalogId 诊疗目录主键 ID
+     * @return 配置的计量单位字符串，若未配置则返回 null
+     */
+    @Select("SELECT total_unit FROM adm_catalog WHERE id = #{catalogId}")
+    String selectDefaultUnitByCatalogId(@Param("catalogId") Long catalogId);
+}
diff --git a/openhis-server-new/openhis-application/src/main/java/com/openhis/web/outpatient/service/OrderMainServiceImpl.java b/openhis-server-new/openhis-application/src/main/java/com/openhis/web/outpatient/service/OrderMainServiceImpl.java
new file mode 100644
index 000000000..186d00446
--- /dev/null
+++ b/openhis-server-new/openhis-application/src/main/java/com/openhis/web/outpatient/service/OrderMainServiceImpl.java
@@ -0,0 +1,61 @@
+package com.openhis.web.outpatient.service;
+
+import com.openhis.web.outpatient.dto.OrderCreateParam;
+import com.openhis.web.outpatient.entity.OrderMain;
+import com.openhis.web.outpatient.mapper.OrderMainMapper;
+import com.openhis.web.outpatient.mapper.CatalogMapper;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.time.LocalDateTime;
+
+/**
+ * 门诊医嘱主表业务实现
+ */
+@Service
+public class OrderMainServiceImpl implements OrderMainService {
+
+    private final OrderMainMapper orderMainMapper;
+    private final CatalogMapper catalogMapper;   // 新增：用于获取诊疗目录配置的默认计量单位
+
+    public OrderMainServiceImpl(OrderMainMapper orderMainMapper,
+                                CatalogMapper catalogMapper) {
+        this.orderMainMapper = orderMainMapper;
+        this.catalogMapper = catalogMapper;
+    }
+
+    /**
+     * 创建医嘱主记录
+     *
+     * @param param 前端提交的医嘱创建参数
+     * @return 是否创建成功
+     */
+    @Override
+    @Transactional(rollbackFor = Exception.class)
+    public boolean createOrder(OrderCreateParam param) {
+        OrderMain order = new OrderMain();
+        order.setPatientId(param.getPatientId());
+        order.setDoctorId(param.getDoctorId());
+        order.setDeptId(param.getDeptId());
+        order.setCatalogId(param.getCatalogId());
+        order.setQuantity(param.getQuantity());
+        order.setCreateTime(LocalDateTime.now());
+
+        // ---------- 修复点 ----------
+        // 之前在保存医嘱时直接使用前端传入的 totalUnit，若前端未传或传入 null，
+        // 页面会显示 “null”。这里改为在数据库层面兜底：如果前端未提供 totalUnit，
+        // 则从诊疗目录（catalog）表中读取配置的默认计量单位并填充。
+        // 这样即使前端忘记传值，也能保证页面展示正确的单位。
+        // ----------
+        String totalUnit = param.getTotalUnit();
+        if (totalUnit == null || totalUnit.trim().isEmpty()) {
+            // 通过 catalogId 查询诊疗目录的默认计量单位
+            totalUnit = catalogMapper.selectDefaultUnitByCatalogId(param.getCatalogId());
+        }
+        order.setTotalUnit(totalUnit);
+
+        // 其余字段保持不变
+        int affected = orderMainMapper.insert(order);
+        return affected == 1;
+    }
+}