A voltage protecting apparatus is used for detecting voltage of a motor driver, and adjusting the voltage of the motor driver when at an over-voltage state. The motor driver includes a direct current (DC) power source and a power board. The voltage protecting apparatus includes a switch unit, a voltage transform unit, a controller, a voltage detector, and an over-voltage judger. When the controller outputs a high level signal, the switch unit is turned on, the voltage transform unit transforms the output voltage of the DC power source to a low voltage. The over-voltage judger receives the low voltage and compares the low voltage to a predetermined voltage. When the low voltage is greater than the predetermined voltage, the over-voltage judger outputs a control signal to the controller for signaling the controller to control the power board so as to adjust the voltage of the motor driver.