During the service period of the casing joints of the injection-production well in the gas storage,the joints of the casing will be subjected to loads such as tensile and compressive loads and pressure in the alternating pipe,which will affect the air-tightness of the casing.To study the contact stress change and distribution law of the main sealing surface of the joint under different working conditions,SOLIDWORKS software and ANSYS software were used to analyze the stress of the special threaded joint of the casing.The wellhead was determined as the dangerous point of casing string air tightness,and the interference of the main and secondary sealing surfaces was also determined.The results show that in order to meet the air tightness and safety requirements of special threaded joints,the interference of the primary and secondary seal surfaces shall be 0.05 and 0.01 mm respectively under high internal pressure.Under low pressure condition,the interference of the secondary sealing surface can be appropriately increased to improve the air tightness.In the actual operation cycle of the gas storage,due to the alternating load,the effective sealing length of the main sealing surface of the joint is changed,even plastic deformation occurs in the stress concentration area,so as to cause seriously damaging the air tightness of the joint.Therefore,it is recommended to use special threaded joints made of high yield strength materials in the gas storage to meet the air tightness requirements of the joints under different working conditions,and appropriately increase the interference of the secondary sealing surface to make the contact stress distribution of the sealing surface more uniform.