content as follows:

<apex:form >
        <apex:commandButton value="删除"  onclick="delMoreIMember()"/>
        <apex:pageBlock >
         <apex:pageBlockButtons location="top">
                <input type="button" class="btn" value=" 删除 " onclick="delMoreIMember()"/>
        </apex:pageBlockButtons>

        <apex:pageBlockTable value="{!existEC}" var="lxr">
            <apex:column >
                <apex:facet name="header">
                    <input type="checkbox" id="allSelectBtn" onclick="selectAll()"/>
                </apex:facet>
                <input type="checkbox" name="ids" value="{!lxr.Id}" onclick="selectOne()" />
            </apex:column>
               <apex:column >
                <apex:facet name="header">电子邮件</apex:facet>
                <apex:outputText value="{!lxr.Field1__r.email__c}"/>
            </apex:column>

        </apex:pageBlockTable>
        </apex:pageBlock>
      
        <script>
            var charray = new Array();
            charray.push("");
            function delMoreIMember(){
                var eids = document.getElementsByName("ids");
           
                var ids = solveParas(eids);
           
                var idslength = ids.length;
                if(idslength<1){
                    alert("请选择至少一条记录");
                    return ;
                }else{
                    var str = charray[0];
                    for(var i=0;i<idslength;i++){
                        str += ids[i]+";";
                    }
                   // alert(str);
                    document.getElementById("{!$Component.gms}").value = str;
                   
                    delMoreItemMember();
                   
                }
                   
            }
        </script>
        <apex:inputHidden value="{!gms}" id="gms"/>
        <apex:actionFunction action="{!delMoreItemMember}" name="delMoreItemMember"/>
      </apex:form>

question:  use <apex:commandButton value="删除"  onclick="delMoreIMember()"/>  ,it doesn't  invoke    method delMoreItemMember in the controller.

               but  like this: <apex:pageBlockButtons location="top">
                <input type="button" class="btn" value=" 删除 " onclick="delMoreIMember()"/>
        </apex:pageBlockButtons>

it can work.  why?can anyone can explain.thanks!