需求：

根据‘是否存在’字段判断‘存在内容’字段是否必填（是：必填；否：不必填）

new Vue({
		data: {
			Rules: {
					isexist: [
						{ required: true, message: '请选择是否存在', trigger: 'change' }
					],
					message: [
						{ required: true, message: '请填写存在内容', trigger: 'change' }
					]
				}
			}
		})

<el-form :model="formxxx" :rules="Rules">
	<el-form-item label="是否存在" prop="isexist">
		<el-radio v-model="formxxx.isexist" label="1">是</el-radio>
		<el-radio v-model="formxxx.isexist" label="0">否</el-radio>
	</el-form-item>
	<el-form-item label="存在内容" prop="message"
				  :rules="formxxx.isexist=='1'?Rules.message:[
					{required: false, message: '请填写存在内容', trigger: 'change' }]">
		<el-input type="textarea"  v-model="formxxx.message"></el-input>
	</el-form-item>
</el-form>