The transmission gear sometimes occur serious wear at high speed conditions because of dry friction,so it is necessary to analyze the film forming properties of automatic transmission fluid at different conditions.The interferometer images of automatic transmission fluid at different load and entrainment velocity were measured with a new nano film thickness measurement instrument,and the film forming properties were analyzed.The film thickness of automatic transmission fluid was calculated,and the calculated results were compared with the theoretical results.The results show that the actual film forming ability of automatic transmission fluid exceeds the Hamrock Dowson theoretical prediction result at different entrainment velocity and load.But under high entrainment velocity，the variation tendency of the actual testing central film thickness is basically the same as Hamrock Dowson theoretical prediction result.By correcting the classical elastohydrodynamic lubrication oil film thickness formula,a elastohydrodynamic lubrication central film thickness formula was put forward.