The section geometric parameters of C-ring sealing structure in pressure holding door was analyzed and optimized by using finite element method (FEM).The sealing property of typical example was calculated and checked.The influence of the section geometric parameters of the C-ring on large gap sealing property was studied.The results show that in the typical example,as the pressure of working medium increases,the contact pressure of the C-ring is increased,and the maximum contact pressure is always larger than the working pressure of medium,so the sealing property of pressure holding door can be ensured.In the large gap sealing condition,the section geometric parameters of the C-ring including the opening radius,opening clearance,and the cutting height have significant effects on the sealing property.The section geometric parameters were optimized according to the analysis results.It is found that the sealing property of the optimized sealing structure under preloading condition and large gap sealing condition is better than that of the original sealing structure.