The invention relates to a test circuit used for a high-voltage DC circuit breaker submodule. The test circuit comprises a controller, a controlled voltage source and a voltage control circuit, wherein the voltage control circuit is used for loading a positive voltage and a negative voltage to both ends of a main loop in the high-voltage DC circuit breaker submodule separately, the controller controls and is connected with the controlled voltage source, and the controlled voltage source is in power supply connection with the voltage control circuit. According to the test circuit, when an electrical path of the DC circuit breaker submodule needs to be tested, the main loop of the DC circuit breaker submodule is connected with the voltage control circuit of the test circuit, a command is issued to the controller, the controller controls the voltage source to output a voltage, the voltage is used for conducting forward power supply and reverse power supply to the main loop in the submodule by means of the voltage control circuit, a capacitor in the submodule establishes an expected voltage when the main loop in the submodule is not conducted, whether the electrical path of the submodule is qualified or not can be judged by measuring a voltage at the capacitor end of the submodule, and the test circuit has the advantages of short detection process, high efficiency, low cost and fast detection speed.