Abstract: During offshore crane operations, the movement of transhipment loads due to adverse sea conditions poses a hazard to nearby workers, or may cause damage to the loads themselves or the surrounding environment. It is a challenging task to control underdrive, the nonlinear system or stable load of a crane. The existing cargo transfer heave compensation equipment has some limitations, such as complex structure, limited compensation range and high cost. Aiming at this situation, this paper proposes a three-degree-of-freedom cantilever compensation mechanism, which combines with the main-auxiliary arm compensation algorithm to realize cargo transfer compensation. Firstly, the influence of crane system transfer under bad sea conditions is simulated and analyzed.Based on the three-degree-of-freedom cantilever compensation mechanism, the kinematics and dynamics model of ship cranes is then built. Finally, the swing compensation is realized through graded compensation control. The simulation results show that, with a compensation rate of as high as 75%, the proposed new compensation mechanism can significantly improve the stability of ship cranes under bad sea conditions, and the operating scope of ship cranes can be expanded.