The invention discloses an automatic power cable unwinding device and an operation method thereof. Among them, the power cable automatic unwinding device includes an installation base plate, a door-shaped stand, a door-shaped stand walking mechanism, an intermediate transfer part, a lifting mechanism, a supporting part, a braking mechanism, a sensing part and a control part. The door-type stand is installed on the installation base plate, and is equipped with a door-type stand walking mechanism. Under the action of the door-shaped stand walking mechanism, the door-shaped stand can move left and right, the intermediate transfer part is used to connect with the cable reel to improve the versatility of the device of the present invention, and the lifting mechanism is used to drive the cable reel to lift When reaching a certain height, the braking mechanism cooperates with the sensing parts, etc., which is beneficial to realize unwinding the cable at a uniform speed. Since the present invention does not directly brake the cable reel, it avoids damage to the edge of the cable reel, and at the same time ensures the smoothness of braking. In addition, the braking precision of the device of the present invention is high.