The occurrence of color dfference in rail transit vehicle body repair s inevitably related to cating,repair process,paint blending and barge treatment Therefore,it is particularly important to do a good job in process control before and afer spraying operation.the problems that it is dificult to repair the Youlan finish of locomotive and the reasons for the color diference of repair spraying and polishing discoloration were briely expounded,so as to provide some references for subsequent operations.