An anti-lock braking system for bicycle connected to the chain stays and the front forks is cooperated with a disk. The characteristics of the brake system is that when the bicycle is stopped at high speed and an initial force is generated, when the initial force is larger than the spring forces in the brake system, the system generates a buffers the initial force so as to prevent the disk from being clamped overly. Therefore, the bicycle is under controlled when it brakes at high speed.