A solution of coordinate measurements of face gear real tooth surface is put forward to obtain deviation in normal direction of surface. It can be used as a basis on determination of accuracy. On the foundation of principle and method of face gear machining

the relative position between tool and gear was analyzed and process coordinates were established. According to the differential geometry and meshing theory

the representation of theoretical tooth surface was established. A set of points for measurements were marked out. The theoretical coordinates and normal vector of points on the grid were calculated. The deviations were obtained after measuring the surface along normal direction. The approach presented in this paper was proved to be accurate.