尝试在商店中设置这些：

Try setting these on the store:

remoteGroup:true,
remoteSort: true

在你的sql或你用来通过分组字段获取数据排序。

And in you sql or what you use to get data out sort by grouping field first.

gridDataStoreObj = new Ext.data.GroupingStore(
{
    remoteGroup:true,
    remoteSort: true,
    proxy: new Ext.data.HttpProxy({url: 'index.php' }),
    method:'POST',
    groupField:'brandName',
    ...     
    sortInfo:{field: 'id', direction: "ASC"},
}); 

在服务器上：

select * from table order by brandName, id

这应该对组本身进行排序。

This should sort groups themselves.