Abstract: [Objectives] In order to investigate the influence of the surrounding water on the process of ship collision, the fluid structure coupling method can better simulate the ship collision process, but the calculation time is long, and the research on the additional mass method is mainly based on empirical formulas, with less experimental research. [Methods] Experimental tests of partial cabin structure impacting by a model ship were performed. The force sensor and the non-contact measurement method based on high-speed photography technology were employed to obtain the impact force and the time history data of the whole collision process. By analyzing the recorded data in detail, the change of the impact force in the collision process was explored and discussed. And the numerical calculations were further performed to simulate the collision process of the tests. A simplified method was proposed to consider the influence of the surrounding water on the collision ship as the "equivalent mass", and treat the influence of the surrounding water on the collided ship as the "equivalent resistance" in the process of collision. Based on this simplified method, numerical calculations that do not involve the coupling process of water and structure are carried out. [Results] The error between the peak value of impact force and the test value is within 5% by using the simplified calculation method, and the calculation time required by this method is less than ALE fluid structure coupling algorithm. [Conclusions] The simplified numerical calculation method can provide some reference for efficient calculation of ship structure collision response.