The present invention belongs to a power module, and especially relates to a submodule for a high-voltage long-pulse PSM power source. The submodule for a high-voltage long-pulse PSM power source is formed by a three-phase diode rectifier bridge, a bus capacitor, a switch tube and a fly-wheel diode, wherein the two input ends of the diode rectifier bridge are connected with a peripheral circuit, asecondary winding is connected with the two inter-bridge positions of the diode rectifier bridge, and the peripheral circuit is formed by a bus capacitor, a switch tube and a fly-wheel diode. The power module is high in level of the output voltage so that the required number of the modules is small in a condition of the same voltage output. The module input is a single-phase alternating current mode, generally, the secondary winding has three phases which can be decomposed into input of three same modules to reduce the volume of a transformer and improve the output voltage level so as to improve the power density of the whole machine.