The information you provided is not specific enough, but I guess this is the reason:

In controller:

$scope.city = {};

In view:

<input ng-model="city.data" />

<li ng-repeat="c in city.data">...</li>

The model must be bound with the city attribute

1. Process the data you want to use on the routing resolve.
2. It is very bad to use $scope.$watch(expression)对你要显示的数据模型进行监测，当数据从远程拉取下来的时候，可以实时更新（不推荐这种方法，在控制器中使用$scope.$watch() on a controller ).

To add to the question, my code is like this

<select name="" id="province" ng-model="group.province.id" ng-change="getCity()">
    <option value="">请选择</option>
    <option value="{{pr.id}}" ng-repeat="pr in prs">{{pr.name}}</option>
</select>
<select name="" id="city" ng-model="group.city.id" ng-change="getDistrict()">
    <option value="">请选择</option>
    <option value="{{city.id}}" ng-repeat="city in citys">{{city.name}}</option>
</select>
<select name="" id="district" ng-model="group.district.id" ng-change="getCircle()">
    <option value="">请选择</option>
    <option value="{{district.id}}" ng-repeat="district in districts">{{district.name}}</option>
</select>

I tried using your method to directly use the repeat object of options as the object of ng-model. It seems that it doesn’t work and an error will be reported

@emj365