C8051F410-based test circuit board was designed according to the test requirement of three-phase power in a certain missile launcher. The phase order, voltage for each phase and frequency for each phase can be tested and the result can be sent to the computer through RS422 communication mode. The hardware and software plan and the development method were described, and different range used different values to fix on the coefficient. The result shows that the circuit has high precision and is reliable, which can greatly improve the efficiency of test.