Aiming at the complex and changeable control factors of shield tail clearance, through the positional relationship between the inner wall of shield tail and the outer wall of segment, the geometric relationship between tunnel curve radius, shield elevation angle, shield tail covering segment length and shield tail clearance was established. Based on the above relationship, the theoretical calculation method of the minimum shield tail clearance was obtained. Moreover, the factors such as tunnel curve radius, shield elevation angle and shield tail covering segment length were analyzed. The results show that the shield tail space is significantly affected when the tunnel curve radius is between 50 m and 400 m. The relationship between the shield pitch angle and the minimum shield tail clearance is nearly linear, and it decreases with the increase of the pitch angle. The length of shield tail covering segment has a more significant effect on shield tail clearance, and the influence on shield tail clearance can be balanced by adjusting the tunnel curve radius and shield pitch angle.