<p>Steering brake squeal is a new phenomenon in the field of brake squeal that requires attention and resolution. In this paper, the deflection of the friction pair is innovatively introduced into the dynamics model of the disc-pad system to study the occurrence mechanism and squeal characteristics under steering braking. This model focuses on the negative friction-velocity slope (NFVS), two-dimensional nonlinear contact characteristics, and cause of deflection in actual disc-pad assemblies. Through the material surface contact theory and finite element method, the mechanisms related to the normal and tangential contact characteristics and the deflection are studied. At the same time, a bench test of the chassis angle module is carried out to reveal the occurrence conditions of steering brake squeal and to verify the accuracy of the model. Based on this model, a new mechanism for steering brake squeal is proposed: the deflection of the brake disc caused by steering, two-dimensional contact parameters, and working condition parameters activate the stick–slip movement of the friction pair, and influence the dynamic behavior of the system, which evolves from decay vibration to a periodic steady-state limit cycle and then develops into chaotic vibration, exacerbating the occurrence of unstable friction squeal. These conclusions can be applied as theoretical guidance for the design and structural parameter optimization of the brake system.</p>