In order to solve the problem that the main drive seal system of shield machine fails in the process of tunneling, which causes damage to main drive, main bearing or gear. Based on the structure and working principle of the main drive sealing system of the earth pressure balance shield, firstly, under suitable field construction condition, the air pressure detection technology for main drive sealing is adopted, that is to inject 100 kPa of compressed air into the inner and outer sealing cavities respectively, after keeping pressure for 30 min, the pressure drop value is qualified when it is within the allowable range, and unqualified when it exceeds, which can judge whether the main drive seal is invalid. Secondly, combined with field experience and theoretical analysis, the causes of seal failure are summarized and analyzed from four aspects of design, assembly, operation and wear. It is concluded that the most common failure causes include unqualified assembly, improper operation and normal wear. Thirdly, in view of the failure causes, it is proposed to prevent and control from design, installation, operation, daily maintenance and other aspects, to ensure the main drive sealing system reach the design service life.