The invention discloses a power transistor driving device with a power-off protection function. The power transistor driving device comprises a driving power supply circuit, a signal isolation circuit, a signal driving circuit, a voltage monitoring circuit and a power-off protection circuit. The signal isolation circuit isolates the control signal of the power transistor from main power applied tothe power transistor. The signal driving circuit outputs a drive signal to control the turn-on and turn-off of the power transistor. The voltage monitoring circuit detects the drive control voltage of the power transistor in real time. When the control voltage is less than a set threshold, the voltage monitoring circuit outputs a low-level signal to the power-off protection circuit. After receiving the low-level signal output from the voltage monitoring circuit, the power-off protection circuit forcibly reduces the drive signal output by the signal driving circuit to a low level, so that thepower transistor is turned off. The power transistor driving device can monitor the control voltage of the power transistor in real time, and turns off the power transistor when the control voltage islower than the normal operating voltage of the power transistor, and avoid the damage to the power transistor working under the non-working voltage.