High pressure safety valve used in aerospace servo system is required to have smaller volume, higher work pressure, more large flow and faster response. Direct acting and high pressure safety valve with spherical sealing structure is one of important structural forms. Although the structure of the safety valve is simple, sealing failure seriously affects product performance, adjusting efficiency and qualified rate. It will affect products delivery schedule and even causes huge economic losses. The sealing failure analysis and improvement was made by theoretical calculations, simulation analyses and experiments. The effectiveness of the improved seal structure was verified by tests.