Abstract: Leakage occurs frequently during the running of water-hammer pilot relief valves. In order to solve this problem, the working mechanisms of the valves were investigated. After many factors were fully analyzed, such as transportation medium, piping process, and environmental temperature, it was pointed out that the leakage was mainly caused by incomplete reset of cone shaped spools, failure of sealing elements and pilot valves and effects of environmental temperature. Finally, a series of solutions were put forward, including regular maintenance, pre-filter and drainage device installation, special inspection on pilot valves and electric heating during operation. When special inspection is performed on pilot valves, it is recommended to judge quickly the integrity of the sealing elements of pilot valves by means of pressurization and carry out off-line pressure stabilization tests and fixed value tests after the inspection. It is demonstrated by the practical operation that the leakage of relief valves can be eliminated by using above mentioned solutions. Based on the pressurization method, the time and difficulty to solve the leakage can be reduced and maintenance efficiency can be increased.