The invention discloses four chassises for a mobile crushing station with a service braking system, comprising a tow bar device (3), a rear axle (5) and a frame assembly (6), wherein the front end of the tow bar device (3) is connected with an equipment tractor (1), and the back end of the tow bar device (3) is connected with a front axle (4), and the tow bar device (3) is internally provided with the service braking system which takes the difference inertia force generated by the four chassises as power when the equipment tractor (1) is braked. The difference inertia force generated by the four chassises when the equipment tractor is braked can be sufficiently used, and the difference inertia force can be taken as a power source of the service braking system by the four chassises, so that not only can the forward impact force to the four chassises when the equipment tractor needs braking in emergency in case of critical situation be effectively avoided, the brake performance of the equipment tractor can be improved, and the parking reliability in the process of service brake can be improved, but also the damage to the equipment tractor caused by the impact force can be further avoided, and the service life of the equipment tractor can be prolonged.