The invention provides a braking-type energy absorber with an initial buffer function and a rubber-tire vehicle derailing preventing method. The braking-type energy absorber with the initial buffer function comprises a base support, a buffer mechanism, a brake mechanism and a roller assembly, wherein the buffer mechanism is arranged on the base support; the roller assembly comprises a roller shaft, brake drums and a roller; two brake drums are symmetrically arranged on the two sides of the roller; the two brake drums and the roller are arranged on the roller shaft. Through the buffer mechanismand the brake mechanism, a frictional resistance gradually increases, and a buffering role that an initial braking force gradually increases is played; when the braking force reaches a design value,hooping steel wire ropes of the buffer mechanism is broken by pull and brake pads do not further hoop the brake drums, so that a friction force is fixed at a design value and a rubber-tire vehicle does not injure people thereon due to a too high braking acceleration.