For a disc brake system, the couples of brake disc and brake pads were supposed to be multi-point contact, and the brake dynamic model with multi-point contact was established considering a semi-empirical theoretical model of a friction coefficient-relative speed curve, which was verified by the rig experiment. Based on the model, assuming that the initial DTV and SRO could be represented mathematically as sinusoidal functions, the influence of the order,the maximum value and the phase of the initial DTV and SRO on brake judder were discussed in detail using the evaluation indicators of the time-frequency characteristics and the root mean square of the BPV and BTV. The results showed that the order of the DTV produces the order for the frequency of the BPV and BTV with the angular velocity; the BPV has the stronger sensitivity to the SRO the and BTV have the stronger sensitivity to the DTV; the roots mean square of the BPV and BTV has linear incremental relations to maximum values of the SRO and DTV; the phase of the SRO influenies the BPV and BTV by changing the maximum value of the DTV.