The citrus were used to extract protein and optimized by the TCA-acedone, Tris-HCl extraction and improved method PBS. The result showed the improved PBS extraction method which was designed by our research group was proved to be suitable and economical to extract the high quality protein from citrus and this facile operation can save time. By research, the improved steps of western blot which include modified protein extraction, SDS-PAGE, trarsmembrane, blocked membranes, antibody incubation and color-reaction were confirmed. It was applied to research the transgenic pthA-nls gene sweet orange plants and it turned out the PthA protein which is related to the Xanthomonas axonopodis pv. citri. is 48 kD protein band。