Localized defects in ball bearing components would cause additional vibration and it is imperative to reveal the vibration mechanism. The relationship between fault characteristic frequency (fBPFI and fBPFO) and multiple defect parameters of ball bearing were given in this paper. Considering elastohydrodynamic lubrication (EHL), radial clearance, time-varying displacement and excitation force generated from multiple defects, a 4 degree-of-freedom (DOF) dynamic model for ball bearing with multiple defects on inner or outer raceway was established, and the model has been verified by experiments. Vibration signals of ball bearing with different defects parameters were simulated, the effects of the angle between two defects (theta(IAD) and theta(OAD)), the number of defects (N-DI and N-DO) and the location of defects on outer raceway on dynamic response were studied. Comparing simulated signals with experimental results, it is shown that more impulses of acceleration signals are generated by multiple defects than that by single defect, meanwhile time delay due to two defects on raceways could also be found, fault characteristic frequency and their harmonics frequencies appeared in the envelope spectrums. Harmonics frequencies of f(BPFI) are modulated mainly by 2f(s) instead of f(s) in frequency domain for multiple defects on inner raceway. The amplitudes of f(BPFO) and f(BPFI) change as Fourier curve when theta(OAD) and theta(IAD) varied within a certain range, and a series of Fourier function are given to describe the mathematic relationship.