Abstract: Collision force and its distribution which acted on the rubber fender of a ship moored to a platform were researched by considering the influence of wind，wave，flow and nonlinear stiffness of the platform fender. According to different angles of wind，wave and flow as well as different wind speed，wave height and flow velocity，the loads of wave and ocean current for mooring system were calculated. And also the analysis model for moored ship was established. Moreover the collision force between the moored ship and a platform were simulated through the method of time domain and frequency domain，and obtained the time history of collision force. Besides，the probability of occurrence of different collision force was analyzed in order to determine the direction of wind，wave and flow which maximum collision force occurred. The results show that the rubber fender stiffness has significant effect on the calculation of collision force， it is essential to choice non-linear fender stiffness when calculating the collision force on the platform. And there are relatively larger deviations by using empirical formula to calculate collision force.