Abstract: The influencing factors of spur gear churning loss include the kinematical viscosity, peripheral velocity and operating temperature of lubricant, module of gear, number of teeth, gear width, oil immersion depth of gear and local gravity values. The coexistence of these factors forms complex functions, and these functions are difficult to determine a direct analytic solution. For the reason, the theoretical analysis of spur gear churning power loss is carried on by using the boundary layer theory of fluid mechanics based on the partial simplification of above factors, and the churning flow partial differential equations are established. By using the multiphase flow VOF model and eddy current K_ε model in FLUENT software, the numerical simulation analysis is carried out. Finally, the simulation results are experimentally verified. The results show that under the condition of low rotation speed, the value of churning power loss can be efficiently predicted by using this simulation method.