A power-down electrical locking protection device for an underground explosion protection frequency converter comprises a reversing control part and a locking control part. The reversing control part comprises a reversing handle (1), a sector plate (2) of a reversing switch, and an isolated reversing switch (3). The locking control part comprises a locking button (4), a locking positioning plate (5), and an auxiliary control point (6). The reversing handle (1) is fixedly connected to the sector plate (2). The reversing handle (1) is connected to the isolated reversing switch (3). The locking button (4) is fixedly connected to the locking positioning plate (5). The locking button (4) is connected to the auxiliary control point (6). A positioning stud (7) is fixed outside a cupboard door (8). The locking button (4) is electrically connected to a PLC module and a power supply. The isolated reversing switch (3) is connected to a discharge resistor. The power-down electrical locking protection device for an underground explosion protection frequency converter has the following advantages: the discharge time does not need to be calculated manually and the usage is stable and safe.