The invention discloses a position detecting device of an electric differential ship unloader. The device comprises an encoder, a transfer case, couplings, a differential detecting gear box, a servo motor, a cover shell, a joint base and a servo driver; the encoder is connected with the transfer case, the differential detecting gear box and the servo motor in sequence through the couplings; a control end of the servo motor is connected with an output end of the servo driver; and an input end of the servo driver is connected with the encoder of a lifting drum in the electric differential ship unloader. The position detecting device of the electric differential ship unloader has basic functions of a differential detecting device, also has a basic function of detecting a lifting height, and is provided with the servo motor and the driver for following up the rotating speed change of the lifting drum in real time; and the position detecting device of the electric differential ship unloader is simple in structure, can randomly distribute the position, can largely relieve the weight of a ship body mechanism, improves the loading and unloading efficiency of the ship unloader, and meanwhile, improves the economic benefit of the ship unloader.