Aiming at the difficulties faced by spacecraft fault diagnosis systems, this paper proposes the basic framework of a fault diagnosis expert system, analyzes the forms of fault rules used in space missions, gives the formal definition of fault rules based on temporal logic, and solves the problem of unified description of fault rules containing time information. A fast calculation method for temporal logic rules is proposed. By defining the logical derivation process of faults, the goal of fault backtracking is achieved. Finally, a fault diagnosis system for space missions is implemented. The system simplifies the process of operators writing fault rules, enables computers to perform fast calculations with a unified logic, reduces the learning cost for operation and maintenance monitoring personnel, and achieves the separation of software developers and software users.