Under the condition of non-newtonian taking a involute spur gear as research object, a gear microscopic surface pitting lubrication model was established, and the oil condition which joined the roughness and thermal factor was introduced. Based on the multi-grid method, a numerical solution of spur gear oil condition lubrication was obtained. The result shows that with the provided oil film thickness increases, the film thickness of the three points also increases. When it is added to a certain degree, the film thickness will no longer change. The result shows that it will not be better as the amount of oil adds, there exists a critical point. Considered the large tooth surface roughness, the numerical results show that asperity leads to the oscillation of the lubricant film thickness and distribution of the pressure, indicating the gear surface roughness is negative for the gear lubrication, the roughness is added to make the numerical solution of the node closer to the actual working conditions.