A reference plate is designed to calibrate surface defects inspecting system. By using it, the defects inspecting system can detect surface defects accurately. The main uncertainty which would affect the system′s measuring accuracy is analyzed to find out the way of reducing it. Electron beam is used to transfer all the design chart to mask plate, and the calibrate plate is produced by using the reactive ion beam etching. Every standard scratch′s actual dimension is measured by scanning electron microscope, and the measured dimension is used to calibrate the surface defects inspecting system. Experiments are performed to calibrate the surface defect inspecting system for large aperture optical components. The result shows that the scattering image is meet to geometrical image result when the dimension of scratch is greater than 45 μm, while it should be computed by calibrated results as the dimension of scratch is less than 45 μm.