To ensure the manufacturing accuracy of a spherical grid, it is necessary to accurately measure the curvature radius, which is one of its important parameters. A measurement system consisting of precision machinery, a microscope, CCD camera, an image processing unit, a grating measurement system, and a computer control is described. By using image processing, noncontact alignment with high speed and accuracy is achieved. The curvature radius of the grid is obtained accurately through applying least-square fitting for multiple points of the grid. The measuring principle and experiments based on the principle are described. The results show that the repeatability of the measurement is up to ±3 ?m.