Abstract: The center insert structure is the key to influencing the mechanical properties of UHV basin insulators. Reasonable structural optimization design can effectively improve the hydraulic failure value and design margin of insulators, and ensure the safe and stable operation of insulators. In this paper, the electric field and stress field distribution simulation model of the basin insulator is established, and different center insert structural schemes are compared. Based on this, the influence of typical structural parameters of the stress release groove and fillet transition line on the interface stress is explored. The optimal structure of the center insert and the hydraulic failure mechanism of the insulator are obtained, and experimental verification is carried out. The results show that convex metal can reduce the stress distribution in the trijunction zone. Furthermore, the stress value at the trijunction point can be reduced by the stress release groove which is deeper and closer to the interface with the appropriate processing width. The phenomenon can be eliminated that the maximum stress is at the trijunction point by using a fillet transition zone. After optimization, the stress value of the trijunction point of the insulator can be reduced by 92.94%, and the maximum interface stress can be reduced by 83.22%. The insulators can still pass the electrical performance test after they have been loaded with 4.5 MPa hydraulic pressure, which verifies the effectiveness and feasibility of the optimized design. The research results can provide a reference for the structural design and optimal control of the basin insulator.