In order to solve the problem that traditional shaft lining design theory cannot reasonably calculate the shaft lining of a shaft with a depth of more than one kilometer, take the shaft lining design of an auxiliary shaft with a depth of 1341.6 meters in Cixi Mine as the engineering background. Through analyzing the mechanical mechanism of the shaft lining and surrounding rock, a unified mechanical model is incorporated into the shaft lining and surrounding rock, and the water and soil coupling mechanism is introduced to establish a mechanical model for the solid-liquid coupling action of the shaft lining and surrounding rock. Based on the thick wall cylinder theory and the third strength theory, the theoretical formula for calculating the thickness of shaft wall under the joint load of shaft wall and surrounding rock is obtained. According to the theoretical expression of joint bearing capacity of shaft wall and surrounding rock, the factors, the factors that affect the reasonable thickness of shaft wall include physical and mechanical parameters such as compressive strength, elastic modulus, shear modulus, Poisson's ratio, and water content and permeability pressure of rock strata. Using this theory, the wall thickness of the auxiliary shaft in Cixi No.1 Mine was calculated: the reasonable thickness of the mudstone section (buried depth 1280m) was calculated as 0.852m, and the design value was 0.9m; The reasonable thickness of the shaft wall in the sandstone section (buried depth 1200m) is calculated as 0.747m, and the design value is 0.8m. Since the design, construction, and use of the shaft, the shaft wall has been in good condition, meeting the needs of safe production. The engineering application shows that the joint bearing theory of shaft wall and surrounding rock and the expression of shaft wall thickness meet the safety design requirements for shaft walls in ultra kilometer deep wells.