Abstract: The real contact area between part surfaces is an importannt issue in tribology.Especially in the state of mixed lubrication,surface contact has important effect on lubricationsituation. Although there were some important outcomes in theritical research about real contactarea 20 years ago,it is difficult to verify the correctness of these outcomes by any effectiveexperimental methods.The anplication of optical method to the measurement of real contact area has made greateffect,but optical method requires that one of the two parts in contact must be transparent body.This requirement restrict the application extent of this technology. In this paper,the acoustic microscope and some other subsidiary installation are used tomeasure the real contact area between steel-ball and sheet aluminium. The acoustic image of realcon tact area has been gotten. It shows that real contact area increases with loading time;the greaterthe load,the bigger the real contact area, because plastic deformation occurs in contact area;lubricants notably influence the measuring result of real contact area.It indicates that the technique of acoustic microscope is a feasible method to detect real contactarea.This method not only overcomes the shortcoming that optical method requires transparentbody, but also can measure the real contact area between two surfaces in relative moving under thecondition of continuous loading in situ, But yet,this method cannot be usedas a quantitativemethod in measuring real con tact area. There are some problems about this method in theory andtcchnique must be resoived.