Hello zhiheng zhu,

Please, check the following topic in our online documentation http://helpdotnetvision.nevron.com/UsersGuide_DockingPanels_Layout_Presistency.html.
Also, you can check All Examples -> Docking Panels -> Layout Persistency example in example application which comes with the installation.

Best Regards,
Nevron Support Team

can you give me some code sample?

i using NDockManager and NUIdocuemnt in my defalut layout and

when i drag the drop the dock panel and add some NUIdocuemnt and change the size of form

how do i restore the default layout?