By assuming the surfaces of two mutual meshed helical gears with continuous cosine wave shape roughness, the steady state model of micro thermal elastohydrodynamic lubrication(EHL)of helical gears was established，and the completely numerical solution was got by using the multiple grid method to calculate the pressure distribution and the grid integration method to calculate the elastic deformation. The influences of the roughness amplitude and wavelength on the film pressure, film thickness and the middle temperature of the film were analyzed．The results show that rough surface is not conducive to the formation of lubrication film, and the film thickness，pressure and temperature hierarchical bulges are appeared in the surface when considering the roughness. The oil film thickness, pressure and temperature are decreased as the wavelength increases, and the oil film thickness, pressure and temperature curves are obviously in fluctuation as the amplitude increases. Therefore in engineering practice, the wavelength of roughness should be increased and the amplitude should be reduced in order to achieve stable mechanical transmission.