The invention discloses a device and a method for automatically testing a break-over voltage of a protection thyristor of an MMC (Modular Multilevel Converter) power module. The device mainly comprises a power supply, a transformer T, a rectifier bridge, an IGBT (Insulated Gate Bipolar Transistor) full-bridge inverter, an electric heating clamp, a voltmeter, an ammeter, a rectifier bridge controller, an IGBT controller and a temperature controller. The device provided by the invention can respectively simulate an actual operation condition of the protection thyristor in an uncontrolled half-bridge power module and a full-bridge power module, can achieve automatic and accurate adjustment of a test voltage by automatically adjusting a trigger angle of the rectifier bridge, can accurately test the break-over voltage of the thyristor automatically, thereby accurately screening the thyristor suitable for the power module, reducing the loss caused by damage of the power module due to breakdown of an IGBT component, reducing the probability that the whole converter is forced to be stopped, and improving reliability of system operation.