The tooth-tips are thinned to increase torque density, which makes tooth-tips saturation occurred. The cogging torque is affected by the magnetic saturation of motor tooth-tips. The effect of tooth-tips saturation on cogging torque is researched in this paper. Firstly, the differences between linear permeability materials and nonlinear permeability materials are expounded from the perspective of energy storage. After that, According to the simulation model, tooth-tips saturation causes air gap flux density distortion and rotor flux density imbalance. When the motor tooth-tips are saturated, the amplitude and period of cogging torque varies by comparing five kinds of tooth-tip materials with different saturation characteristics.