Abstract: This paper analyses the space total dose effects of three MOSFETs (IRF5N3415, IRF7NA2907, IRF7N1405) in a secondary power supply on the space payload. The process of the anti-radiation design is discussed. In order to make the radiation design margin (RDM) larger than three, the radiation hardening technologies such as the tantalum sheet hardening and reasonable structure re-arrangement are used. Through total dose radiation test, the electrical performance data of the three MOSFETs are obtained by comparing the variations of the main parameters before and after the test, which prove the effectiveness of the design. The use of non space-level components will become a new tendency for low cost space applications in the future.