Abstract: Through the analysis of gear lubrication mechanism, the change law of relative sliding speed on the meshing line of gear pair is revealed. According to Dowson-Higginson's empirical formula of minimum oil film, the laws of equivalent curvature radius and entrainment speed changing with transmission ratio and modification coefficient, which are key factors affecting gear lubrication performance, are analyzed. Based on accurate tooth profile, the distribution of tooth surface load along the meshing line is calculated. The influence of gear design parameters such as transmission ratio, modification coefficient, pressure angle and center distance on the minimum oil film thickness of gear pair is analyzed by programming and calculating the corresponding relationship curves. The results show that the transmission ratio makes the minimum oil film thickness curve incline and rotate, the modification coefficient determines the starting and ending points of the film thickness curve along the meshing line, and causes the change of the center distance of the gear pair to indirectly affect the minimum film thickness. The relationship between the center distance, pressure angle and the minimum film thickness is positive correlation. Finally, the gear lubrication state is judged according to the film thickness ratio relationship. It can be seen from the calculation curve of an example that the minimum oil film thickness point of the gear pair does not occur at the meshing point of the pinion tooth root and the big gear tooth top, so the oil film thickness ratio of the meshing node is used to determine the gear lubrication state. The above conclusion provides a reference for the design of elastohydrodynamic lubrication of gear transmission.