Abstract: In this paper, an evaluation method for the deformation and airtightness of the external passageway of a ship collective protection system is presented, where the seal structure like doors and windows is selected as the research object. Firstly, long-term prediction of ship's cross-sectional wave-included loads is conducted based on spectral analysis. Next, the parameters of designed waves are determined, and with FEM software MSC/PATRAN, a FEM model of the ship is established. The designed wave pressure is automatically applied to the ship's wet surface elements through PCL language. After obtaining the result of the deformation of the external passageway, a FEM model of sealed structures is built, where the 3D model of deformed doorframe are calculated based on the result of the general ship FEM model. Finally, contact analysis is conducted between sealing strip and the doorframe, and the result under normal contact stress is compared with the given value to evaluate the airtightness of the sealed structure. It can be concluded that the proposed method serves as a good reference to the ship design that has similar requirements.