<p>Tooth root bending fatigue failure is the most dangerous form in gear transmission, which seriously affects the safety of machine and human. This study aims to investigate the gear root crack propagation behavior and fatigue life. A crack propagation model was established based on pulsating tooth root bending strength fatigue test by using ABAQUS combined with FRANC3D, and was verified by experimental tests. The influences of the initial crack position, crack length, and crack direction were discussed. The results indicate the initial crack position has significant influence on both the propagation path and fatigue life. As the initial crack location approaches the tooth tip, the propagation path is gradually parallel and approach, and the fatigue life first decreases and then increases. Meanwhile, the initial crack direction and length have minimal effect on the propagation path, but the fatigue life decreases as the initial crack length increases.</p>