The invention relates to a bridge type four-reel grab bucket type electrical differential system for a ship unloader. The system comprises a control system, a main body framework, an operation controlmechanism, steel wire ropes, pulleys, a trolley and a grab bucket, wherein the operation control mechanism comprises four sets of driving mechanisms with the same structure, and the driving mechanisms respectively comprise speed reduction boxes, reels, motors and brakes in the same structures; the pulleys are arranged on the main body framework; the steel wire ropes are connected with the grab bucket, bypass through the pulleys through the trolley and wind the reels; and the control system is used for controlling the operation control mechanism so as to control the lifting, opening and closing of the grab bucket through the steel wire ropes and the operation of the trolley. By utilizing a modular design, the structural form is relatively simple, and parts have very high universality, interchangeability and maintainability.