Abstract: In order to find out the key factors affecting the precision of nitrogen surge relief valve's set pressure, mechanical relation equation affecting critical set pressure of nitrogen surge reliever is established on the basis of its structure and operation principle. It is shown that the precision of nitrogen surge relief valve's set pressure is mainly influenced by the precision of pressure reducing valves, the effect of environmental temperature on nitrogen pressure, the friction on the piston body, the design of the seat sealing structure and the stability of the spring stiffness. Some methods are provided to control the precision of set pressure. It is revealed by the test results that the precision of set pressure reaches ±1% after the nitrogen surge relief valve are improved on the basis of the theories proposed in this paper.