A padlock comprises a bolt unit having a stopper, a brake unit being moveable up-and-down, and a drive unit for driving the movement of the brake unit. The drive unit includes a drive motor and a driving cap fixedly sleeved on a drive lever. The driving cap includes a lug boss. The brake unit includes a first spring fixedly connected to a tumbler. The spacing of the coils of the first spring matches the lug boss such that the lug boss can move inside or outside of a threaded gap thereof. After the padlock is locked or unlocked, even if the drive lever continues to rotate, the lug boss just moves out of the first spring and may not drive the first spring to move up or down. Thus, the tumbler stops moving up or down and will not generate a pressure on the internal structure of the padlock.