This paper presents numerical studies of analyses of the limit cycle of the reaction control system (RCS) and their validations through hardware-in-the-loop simulation (HILS). The numerical analyses under external disturbance and time-delays of the thruster are confirmed experimentally by HILS for an attitude control system with a single degree of freedom. The thrust of each jet thruster is determined from offline vacuum test results instead of actual thrust measurement. The comparison of HILS results with numerical analysis, shows that predicted properties of the limit cycle is closed to the test results, thus it can be applicable to real RCS. The HILS method allows us to test the RCS without an air-bearing system.