Abstract: The meshing process of the spiral bevel gear was simplified to the point contact between several curved surfaces and a plane． A similarity model subject to elastohydrodynamic lubrication was established by using the similarity theory． The model was then verified by the elastohydrodynamic lubrication theory． The influence of the different parameters on the system similarity was investigated． The analysis results show that under the premise of meeting the similar criteria，changing the entrainment speed and the viscosity of the lubricating oil has little influ- ence on the similarity degree; When the load，the pressure-viscosity coefficient，the radius of curvature and the e- lastic modulus are changed，the similarity error of the system becomes larger; the more the parameters change，the more obvious the error stacking effect is． Selecting the parameters reasonably according to the similarity model， the film thickness and its distribution in the meshing zone of the spiral bevel gear pair can be indirectly measured by the optical interferometry method． Finally，the experimental data were compared with the similarity model results． The result shows that when the entrainment speed is less than 1 m /s，the similarity model results are close to the experimental results，and the maximum error is 12. 82% ; when the entrainment speed changes greatly ，the simi- larity model results have large deviations．

Key words: spiral bevel gear, similarity model, elastohydrodynamic lubrication, system similarity, film thicknes, entrainment speed