Sealing is one of the key technologies of deep-sea pressure compensator. In order to accurately analyze the sealing performance of the structure，which composed by flange，film gasket and bolt，on the sea and under deep-sea environment, the three-dimensional (3-D) structure model was established by using of the ANSYS software. The film gasket pre-stress was calculated to analyze the sealing performance of the gasket and some factors which influenced the sealing performance were taken into account, such as the depth，pre-tightening force and installation position of the bolt，thickness and width of the diaphragm，and etc. The results indicate that: in order to meet the sealing requirements, the bolt pre-tightening force must be greater than 4 500 N on the sea, and the gasket stress depends on the depth and the stress is in consistent with the environmental pressure under deep-sea.