Abstract: Special thread joint oil tube for high pressure gas well has leaked out, combined with the oil tube leakage inspection results, the causes of oil tube leakage were analyzed by means of chemical composition analysis and mechanical property test. The results show that the leakage of the sealing face of the oil tube was mainly concentrated in the 3 900-4 869.49 m section, and the 4 200-4 500 m section of the seal face of the oil tube was all leaked. The leakage of the sealing face of the oil tube was related not only to the bending load, but also to the stiffness of the oil tube. The oil tube that permeates from the end of the coupling surface was concentrated in the 1 800-4 869.49 m well section, the reasons might be related to the change of the performance of the thread grease after the temperature rises or related to the load distribution under the oil tube. The leakage of multiple oil tube joints shows that the gas seal performance of this type oil tube was not in conformity with the requirements of the well.