Put these properties to the 'data-options' attribute.
<SELECT class='easyui-combobox' panelHeight='auto' label='Category' editable=false data-options="width:320,labelWidth:90">
</SELECT>
Or
<SELECT class='easyui-combobox' data-options="width:320,labelWidth:90,label:'Category',editable:false,panelHeight:'auto'">
</SELECT>
If you really want to use the 'width' attribute on the element, please override the $.fn.combobox.parseOptions function to support it.
<script type="text/javascript">
(function($){
var oldParser = $.fn.combobox.parseOptions;
$.fn.combobox.parseOptions = function(target){
return $.extend({},
$.parser.parseOptions(target, [{width:'number'},{height:'number'}]),
oldParser.call(this,target)
);
}
})(jQuery);
</script>
Now the code below works well.
<SELECT class='easyui-combobox' panelHeight='auto' label='Category' editable=false labelWidth=90 width=320>
</SELECT>