Abstract: The special research is carried out on the leakage problem of the safety valve used in the field test. The main failure cause of safety valve has been found by dismantled them into parts, by checking the surfaces and the major dimensions, and analysis and inspection of the initial reason, measuring the coaxiality, then comparative tests for the relief valve, changing the parts, testing of airproof performance at cold state and hot state. According to this, the corresponding improvements has been taken to the 4 safety valve for repairing. The main cause of the problems that obtained and the improvements is accurate and appropriate from the testing results of the equipment and the submarine. According to the checkouts and tests results of products that hand over recently, the quality and the reliability of the safety valve has been improved evidently.