The utility model discloses a letter sorting system of part after numerical control unloading, including host computer, PLC controller and gantry crane, wherein, gantry crane includes the manipulator,the end of manipulator is provided with automatically controlled permanent magnet, automatically controlled permanent magnet through a rotary mechanism with the end -to -end connection of manipulator, the manipulator automatically controlled permanent magnet with rotary mechanism respectively with PLC controller electric connection, the PLC controller still with host computer communication connection. Adopt the embodiment of the utility model provides a, the letter sorting efficiency of part can be improved, intelligent, automatic unmanned sorting operation is realized.