Based on elasticity theory, the stress field and stress intensity factor of gear crack are discussed. The effect of friction coefficient and crack shape on equivalent stress, displacement at crack tip and stress intensity factor were analyzed by using general finite element software ANSYS, and the formula of stress intensity factor of gear crack was revised. The results showed that the equivalent stress, displacement at crack tip and stress intensity factor increased with the friction coefficient for the same crack. For the same f and different a/c, the front friction surface played a major role when a/B﹤0.05, and the post friction surface played a major role when a/B﹥0.05. The stress intensity factor increase at first, and then decrease with the increase of a/c.