如果是直接绑定属性，是可以的，但是绑定对象中的属性就需要特别处理，需要在rules中添加双引号 " "

<template>
  <div class="about">
    <el-form :model="ruleForm" :rules="rules" ref="ruleForm" label-width="100px" class="demo-ruleForm">
      <el-form-item label="活动名称" prop="name">
        <el-input v-model="ruleForm.name"></el-input>
      </el-form-item>
      <el-form-item label="活动区域" prop="region">
        <el-select v-model="ruleForm.region" placeholder="请选择活动区域">
          <el-option label="区域一" value="shanghai"></el-option>
          <el-option label="区域二" value="beijing"></el-option>
        </el-select>
      </el-form-item>
      // 注意这里
      <el-form-item label="活动形式" prop="activity.type">
        <el-input v-model="ruleForm.activity.type"></el-input>
      </el-form-item>
      <el-form-item>
        <el-button type="primary" @click="submitForm('ruleForm')">立即创建</el-button>
        <el-button @click="resetForm('ruleForm')">重置</el-button>
      </el-form-item>
    </el-form>
  </div>
</template>

<script>
  export default {
    data() {
      return {
        ruleForm: {
          name: '',
          region: '',
          activity:{
            type:""
          }
        },
        rules: {
          name: [
            { required: true, message: '请输入活动名称', trigger: 'blur' },
            { min: 3, max: 5, message: '长度在 3 到 5 个字符', trigger: 'blur' }
          ],
          region: [
            { required: true, message: '请选择活动区域', trigger: 'change' }
          ],
          // 注意这里
          "activity.type": [
            { required: true, message: '请输入活动名称', trigger: 'blur' },
            { min: 3, max: 5, message: '长度在 3 到 5 个字符', trigger: 'blur' }
          ],
        }
      }
    },
    methods:{
      submitForm(formName) {
        this.$refs[formName].validate((valid) => {
          if (valid) {
            alert('submit!');
          } else {
            console.log('error submit!!');
            return false;
          }
        });
      },
      resetForm(formName) {
        this.$refs[formName].resetFields();
      }
    },
  }
  </script>