i create a 300x300 transparent form using setwindowlong and setwindowpos to
make it transparent and topmost, when the windows below this form is moving
outside, the windows will not redraw and stick with the graphics of the
floating form

and when some windows is moving inside, the graphics of the form will
disappear, how to solve that?

Hello,

You can use the Form.TopMost property to make a window top-most.

If you want to make a window transparent, set the window region by
manipulating the value of the form's Region property or the form's
TransparencyKey property.

Regards,
Herfried K. Wagner