I have a problem about the sgdma when I used it to transfer vga data(800x600x4bytes)!

That looks like a photo of a CRT. If you can find an LCD panel (particularly one with the correct native resolution) single pixels will be much easier to see

(This is most obvious when using direct digital interfaces to LCD panels).

I can think of two possibilities:

1) You don't have the correct parameters for the vidoe frame (front and back porches etc), possibly the display isn't actually showing the first few data lines (ie the image is too high up the screen)

2) The program wrote the data via the data cache, and the data for the last few lines hasn't been written to physical memory.

Changes to the test image and the order in which the image is written to memory might help identify the problem.