Thx for the input.
I also found another way, here it is:
jquery.easyui.min.js add this:
$.extend($.fn.datagrid.methods,{
	resizeColumn:function(jq,param){
		return jq.each(function(){
			var dg = $(this);
			var col = dg.datagrid('getColumnOption', param.field);
			col.boxWidth = param.width + (col.boxWidth-col.width);
			col.width = param.width;
			dg.datagrid('fixColumnSize', param.field);
		})
	}
})Then the onEdit will work with this:
var ed = $(this).edatagrid('getEditor',{index:index,field:'comment'});
			$(this).datagrid('resizeColumn', {
                       field: 'comment',
                      width: 300
});