It is said that the disc brake squeal is the noise caused by the friction-induced vibration between pads and rotor, by which the brake assembly resonates. In this paper, the forces on the pads and the accelerations of the brake were measured, and their results were discussed by the correlation of them. As a result, the forces acting on the pad were observed to vibrate at low cycle synchronizing with the revolution of rotor. And the friction coefficient curve indicates several parts of negative gradient and periodicity. This phenomenon was well correlated with the mechanism of the excitation of brake squeal vibration by the simulation result.