The invention discloses an avalanche energy tester of a power MOSFET device, comprising a front-end avalanche testing circuit and a back-end avalanche current sampling circuit. The hardware structure of the front-end avalanche testing circuit comprises an adjustable direct current power supply which is connected with a fuse, an MOSFET device, an inductor, a current sensor and an MOSFET device to be tested successively to form a circuit; an electrolytic capacitor and a ceramic capacitor are paralleled between the drain electrode of the MOSFEF device and the source electrode of the MOSFET device to be tested; a diode is connected between the source electrode of the MOSFET device and the source electrode of the MOSFET device to be tested; and the structure of the back-end avalanche current sampling circuit is as follows: a signal conditioning circuit and a reference source circuit are connected with an analog-to-digital converter, and the analog-to-digital converter is connected with an FPGA control logic which is respectively connected with a test machine signal connector, an MOS driving circuit and a separator signal connector. The tester in the invention can provide high instantaneous current to test the avalanche energy.