Abstract: The analytical geometry of a face gear and the mathematical model for face gear error analysis are established based on the face gear generation process.The normal vector of each point on the surface of the face gear is also obtained.The error caused by the coordinate disunity of the face gear and the CMM is analyzed.The datum of the point measured on the surface of the face gear is not the inspection datum of the center of the probe.A corresponding equation is put forward to compensate for the error caused by the disunity of the measured point and the center of the probe.