我使用这样的css类来定位modal-dialog类：

.app-modal-window .modal-dialog {
  width: 500px;
}

然后在调用模式窗口的控制器中，设置windowClass：

    $scope.modalButtonClick = function () {
        var modalInstance = $modal.open({
            templateUrl: 'App/Views/modalView.html',
            controller: 'modalController',
            windowClass: 'app-modal-window'
        });
        modalInstance.result.then(
            //close
            function (result) {
                var a = result;
            },
            //dismiss
            function (result) {
                var a = result;
            });
    };