For the purpose of detecting 3D geometric topography of an arc diamond wheel precisely and efficiently in aspheric element processing, the methodology of on-machine measurement and the error evaluating of 3D geometric topography were proposed. Firstly, the mathematical model of screw-scanning track for the diamond wheel was established, and the profile data of the diamond wheel were acquired by a displacement sensor. After data filtering and interpolating, the 3D geometric topography of the diamond wheel was established. According to the feature of aspheric parallel grinding, some parameters to criticize the shape accuracy of arc wheel were put forward. By extracting the wheel profile of the axial direction, the arc radius and center coordinates were calculated by least-square circle fitting. And by error segregating, arc error, circular runout error and the deviation of profile center for the diamond wheel were extracted. Finally, an arc diamond wheel in aspheric element processing was measured experimentally. Some key dimensions and errors of the diamond wheel were achieved. The average radius of the wheel is 55.442 3 mm and the fluctuation range of radius is 0.16 mm. The arc error in the girdle of ±8 mm is about 5 μm, the circular runout error is about 2 μm and the relative deviation of profile center is 0.008 mm. By using those measured data, a large scale aspheric optics grinding experiment was performed and results show that the surface errors( P-V and RMS) of the element are about 4.62 μm, and below 0.7 μm, respectively, which satisfies the engineering requirements.