The invention discloses a full-trailer braking system and a braking method thereof. The full-trailer braking system comprises a braking air supply pipeline, a traveling braking control pipeline, a parking braking control pipeline, an ABS system and a pipeline connecting all parts. The braking air supply pipeline is connected with a braking air supply pipeline of a tractor to provide pressure air for the full-trailer braking system. The traveling braking control pipeline is connected with a traveling braking control pipeline of the tractor to provide control pressure for traveling braking of a full-trailer. The parking braking control pipeline is connected with a parking braking control pipeline of the tractor to provide the control pressure for parking braking of the full-trailer. The full-trailer braking system can be directly operated by a driver in a cab; meanwhile, the full-trailer braking system has the ABS anti-lock function and has a self-adaptive ability to different suspension loads and braking force.