The noise of disk brake pair has always been a difficult problem for enterprises and researchers. Many factors induce the noise of disk brake pair, among which the influence of the third body particle flow generated by the external gravel or its own abrasive debris has not been paid much attention. Three-body contact has different friction properties and requires a new friction model to describe it. This paper presents a friction model of disk brake pair on the basis of the predecessors. The new model further considers the influence of the third body on the nonlinear behavior of the brake system on the basis of the previous model of the brake pair. Through numerical simulation, it is concluded that the geometry size of the third body has great influence on the stability interval of the braking system. Finally, the influence of the third body particles on the motion stability of the braking system under different particle size ranges is studied. It is found that larger particle size can improve the motion stability of the system.