Abstract: The research the object is precision shafting in spacecraft mechanism. The Life prediction mathematical model of space bearing is established and the method for optimizing the initial preload of solid lubrication bearing is proposed. It provides theoretical guidance for the design and selection of the bearing preload. Based on the kinematics, quasi-static analysis of the rolling bearing and Archard wear model, the requirements for the stiffness and ultimate pressure resistant bearing capacity of lubricating layers are considered. Thus, the allowable range of preload is determined. With the optimization objective of the longest service life, the initial preload of the space bearing 71807C is optimized. The results indicate that the selection range of the initial preload for space bearing is from 70 N to 200 N. During the wear process, there is a correlation between the wear depth and residual preload. Based on the longest lifetime optimization, the optimal initial preload of the precision shafts system is obtained, which is 156 N. The failure mechanism of the bearing is analyzed under various preloads.