The invention provides a spur gear tooth root crack propagation rule analysis method based on finite element simulation. The method comprises the following steps of firstly, establishing a gear simulation model by utilizing ANSYS, then completing load loading, mesh generation, boundary condition setting, stress solving and other work on the basis of the model, importing the model into FRANC3D to obtain data such as an expansion path and direction of a gear tooth root crack, stress intensity factor change in a crack expansion process, crack life prediction and the like, and finally, analyzing afinite element simulation result to obtain a spur gear tooth root crack propagation rule. According to the method, the propagation rule of the spur gear tooth root cracks is researched based on a numerical simulation method, the crack propagation situation is tracked, the distribution rule of crack tip stress intensity factors and a fatigue life prediction curve are obtained, the calculation precision is high, the experiment speed is higher, the efficiency is higher, and convenience is brought to the depth research of gear tooth root crack propagation.