The hardware functional modules of relay protection CPU board are analyzed. The automatic test system of CPU board has good universality and practicality, which is designed with the idea of modularization and hierarchy, and the hardware structure of the automatic test system is described in detail. According to the characteristics of CPU board hardware function modules, they are divided into three categories, and testing methods and testing processes of various functional modules are expounded respectively. Combined with a specific application case, the present application situation is introduced. It has achieved sound use effect in the production test of CPU board, and greatly shortens the test time in the production process of relay protection of CPU board.