Hi Lincy,
This could be easily resolved by using AutoLayout property of the FlowLayoutManager. Setting AutoLayout to false, will resolve the issue.
[Code]
this.flowLayout1.AutoLayout = false;
[Sample]
http://websamples.syncfusion.com/samples/Tools.Windows/F60836/Main.htmPlease refer to this and let me know if it helps you.
Thank you for your interest in Syncfusion products.
Regards,
Murugan P.S