The space high-energy particle radiation has a serious influence on the reliability of the space computation. Effective radiation hardening measures must be taken to overcome this problem. Compared with the use of radiation hardening devices, using the soft reinforcement commercial devices can enjoy the advantages of high performance, low cost, fast development and so on. However, the present research on soft reinforcement is mainly suitable for the application level, while there is very little research on soft reinforcement methods for the operating system. A control flow checking method for the on-board operating system was proposed to solve this problem. Taking account of the characteristics of the on-board operating system, the proposed method regarded each thread as a sequence of function calls and monitored the thread execution through inserting test statements in the entry and exit of a function to achieve the control flow error detection. The experimental results indicate that the proposed method can increase the control flow fault coverage of the on-board operating system by 25%.