Sembazuru:
Too little information. Which WiFi module (there are several)? How do you communicate with the WiFi module (SPI, SoftwareSerial, or Serial)?If (as I suspect from the error) it is Serial you need to disconnect the WiFi module while you are uploading a new sketch to your Mega. Otherwise the WiFi module is also responding to the communication between avrdude and the 2560 confusing everyone in the process.
yessssss, you are right,i don't realize to remove the wifi module when i upload the program. thank you very muchhhhh~~~~