Edit in JSFiddle

<form name="form1" ng-app="">
    <input type="email" name="email" ng-model="email" placeholder="請輸入email" />
    <span 
       ng-class="{'alert':form1.email.$error.email}"
       ng-show="form1.email.$error.email">
        email格式錯誤
    </span>
</form>

.alert {
    color:red;  
    display:inline;
}