这里有问题吧！

你把tigger函数放在change函数体后面再试试。

//jQuery插件
<script type="text/javascript" src="./scripts/jquery-1.6.4.js"></script>
//代码
$(document).ready(function(){
                //添加附件按钮                
                $("#selectFileBtn").click(function(){
                    $fileField = $('<input type="file" name="thumbs[]"/>');
                    $fileField.hide();
                    $("#attachList").append($fileField);
                    $fileField.trigger("click");
                    $fileField.change(function(){
                    $path = $(this).val();
                    $filename = $path.substring($path.lastIndexOf("\\")+1);
                    $attachItem = $('<div class="attachItem"><div class="left">a.gif</div><div class="right"><a href="#" title="删除附件">删除</a></div></div>');
                    $attachItem.find(".left").html($filename);
                    $("#attachList").append($attachItem);        
                    });
                });
                //<div class="attachItem"> 删除
                $("#attachList>.attachItem").find('a').live('click',function(obj,i){
                    $(this).parents('.attachItem').prev('input').remove();
                    $(this).parents('.attachItem').remove();
                });
            });