Impact phenomenon exists widely in mechanical components such as rolling element bearings and industrial chains,which can cause impact wear in the worst case.To investigate the effect of impact load on film formation under grease lubrication conditions,impact tests were carried out to study the grease film thickness evolution under lithium grease lubrication on a point contact optical interferometric test rig.During the experiment,the initial distance between the steel ball and the glass disk is set to zero and the load repeatedly varies in the form of a triangle wave.The results indicate that during the first impact period,there exists big lump of thickener fibers in the contact area,which results in an entrapment of the grease film.With the increase of the impact periods,the big lump thickener disappears,the film thickness is gradually reduced and lubrication state turns to be thin film lubrication.At last,surface damage occurs in the surfaces of both the steel ball and the glass disk.In each impact period,either central or minimum film thickness mainly exhibits a constant value.The central film thickness decreases with the increase of the impact periods.The minimum film thickness varies only slightly in the first 100 periods and gradually decreases to zero.