Abstract: It is extremely important to accurately determine the ship mooring collision load in considering ship and offshore platform's strength. This paper proposes a method to determine the ship mooring collision load with energy principle and the finite element method. In collision, the impact kinetic energy and the deformation energy are considered in the energy conservation law. The kinetic energy refers to the ship's kinetic energy including the additional water mass. It is transformed into the deformation energy when collision occurs. That collision load can be calculated by the relationship between the deformation energy and the load. The theoretical solution of abeam is used to validate the method. The method can be used to determine the impact force of the fender in practical cases.