Abstract: The reliability of spacecraft assembly is a key factor for improving the quality and efficiency of spacecraft assembly. Based on the characteristics of spacecraft assembly, this paper proposes a new reliability theory, including the modeling and analysis of the assembly procedure, the theory of reliability apportionment, and the assembly process FMEA theory, to evaluate the assembly process of spacecraft. Analysis results demonstrate that these reliability concepts and methods are effective for finding the potential fault models to improve the efficiency and quality of spacecraft assembly.