Abstract:According to the practice that involute spur gears often work under the mixed elastohydrodynamic lubrication, a theoretical model of dynamic friction coefficient under mixed elastohydrodynamic lubrication was established based on the analysis on forces from meshing surfaces, which was a combination of elastohydrodynamic lubrication and boundary lubrication friction coefficients. A math model of sliding and rolling friction power loss was established with a variable of pressure angle, which erased the principle error of the prevailing power loss integral calculation. Finally, the simulation of power loss model was employed and compared with the test value, which verified the feasibility of meshing efficiency model of involute spur gear under the mixed lubrication.