The invention provides a rear axle braking device, an axle braking system and method as well as a vehicle. The rear axle braking device comprises a rear axle relay valve, a rear axle braking air chamber, a rear axle braking air storage barrel, a pipeline control valve and a foot braking valve, wherein a working gas output opening of the rear axle braking air storage barrel is connected with the rear axle braking air chamber through the rear axle relay valve; a control gas output opening of the rear axle braking air storage barrel is connected with a first control opening of the rear axle relay valve through the pipeline control valve; and the foot braking valve is used for controlling the switching-on/off of the pipeline control valve. According to the rear axle braking device disclosed by the invention, control gas of the rear axle relay valve does not need to wind around the foot braking valve in a cab, so that the hysteresis of the rear axle relay valve is not caused as a control gas pipe is lengthened; a phenomenon that the braking of a front axle is ahead of the braking of a rear axle is avoided, so that the braking synchronization of the front axle and the rear axle is improved and the braking effect of the whole vehicle is enhanced.