The diameter change of the spherical grinding wheel after on-site dressing may lead to position deviation between ideal and actual grinding trajectory, which bring the machining error. Therefore, it is very necessary to obtain the change information before ultra-precision grinding. In view of this, this article proposes an on-site measurement scheme of the spherical grinding wheel, including the establishment of the on-site measurement system based on the laser tool presetter and on-site measurement steps design. The systematic error of this scheme is analyzed, the installation error model of laser tool presetter is abstracted, the error formula is deduced combined with homogeneous coordinate transformation, and the installation error is solved by the least square method. Therefore, the compensation of measurement data and high-precision on-site measurement of the spherical grinding wheel are realized. Finally, the standard ball with 12. 5 mm radius is used for calibration, and the error angle value is calculated for compensation. Then, the 12. 5 mm and 3 mm standard balls are measured for verification. Experimental results show that the measurement accuracy can be improved from 4 μm to 1. 2 μm.