The structural characteristics and performance requirements of the threaded plug-in relief valve were analyzed,and the factors affecting the accuracy of the relief valve were determined as the static and dynamic characteristics of the relief valve,the fill-in opening pressure,the tightness,and the manufacturing requirements based on a specific process.By analyzing the above factors one by one,the accuracy requirements of each factor for inner cone surface were obtained.A model was established and analyzed according to the specific process requirement of grinding after carbonitriding,and the precision requirement of the inner cones own angle was obtained.The application analysis for the model was carried out and the optimal value of the inner cone angle accuracy was obtained after feedback adjustment.The results show that the main factors affecting the design and manufacturing precision of inner cone are the sealing and the manufacturing requirements based on specific process;according to the structure and design parameters of the relief valve,the shape accuracy of the inner cone is required to be 5~6 grades (0.001 5~0.002 5 mm),and the runout of the inner cone relative to the mating inner hole is required to be 0.012~0.015 mm;the accuracy of the angle of the inner cone is required to be ±1°,and the axial dimension tolerance of the corresponding contact circle is 0.052~0.186 mm.The test results show that the static and dynamic characteristics and service life of the valve sleeve obtained according to the design accuracy requirements meet the relevant requirements.