When the sealing structure has size deviation,the compression ratio of the O-ring will change accordingly.The contact pressure distribution of nominal size corresponding to the compression ratio can not be used as a reference index to measure the sealing performance of the sealing structure at the moment.In order to study the influence of structure size deviation on sealing performance,the control variable method was used to analyze the contact pressure distribution of O-ring with the change of sealing structure size deviation based on the mechanical simulation model of components.Taking the maximum contact pressure as the control parameter,through the mechanical simulation analysis of different size combinations,the worst size combinations to minimize the maximum contact pressure were obtained.According to the fit between the lower baffle and the groove at different distances,the leakage rate was taken as the evaluation index,and the influence of vibration on the fit between the baffle and the groove in the operation process was analyzed by comparing the sealing performance of the O-ring under different fit gaps,thus laying a foundation for the selection of the assembly combination of the O-ring and the study of the contact situation of the sealing surface.