Hi Kai,
The Group CaptionText can be customized using the TableDescriptor.ChildGroupOptions.CaptionText property (gridGroupingGrid.TableDescriptor.ChildGroupOptions.CaptionText = "{CategoryName}: {Category}";). The QueryCellStyleInfo event can also be handled to have your own text in the group caption row. Please refer to the below forum for more details.
http://www.syncfusion.com/Support/Forums/message.aspx?MessageID=11530
Regards,
Calvin.
