Abstract: In order to reduce the accident risk caused by casing leakage in oil and gas well, the oil field adopts the gas seal detection technology to check and detect the leakage of completion casing, so as to ensure the integrity of casing. The principle, standard, current situation, detection pressure and detection time of gas seal detection in tarim oilfield were analyzed, and some test reports were extracted to analyze the causes of unqualified casing detected by gas seal detection. The results show that the proportion of qualified casing re detection was large after shackle, cleaning, smearing thread grease and eliminating external interference. Due to the small proportion of leakage caused by thread damage or quality factors, it was considered that the main factors causing unqualified casing gas seal inspection were site operation and service environment. The gas seal detection technology can provide technical guarantee for the gas tightness of the joint factory end, and solve the problem of lack of detection means for the factory end in the oilfield. Compared with the serious consequences caused by joint leakage, although the running time of each casing is increased by nearly 4 min, the gas seal detection is still an indispensable process. The leakage rate will not increase with the increase of the detection pressure, and has no direct relationship with the detection pressure. When the detection pressure is 60% of the internal pressure strength of the casing, it is safe and reliable.