A method based on spectral estimation and a multispectral technique is proposed to accurately and efficiently measure surface efects of optical elements. Using this method, we estimate and obtain single spectral defect images at different wavelengths and compose a multispectral defect image from different single spectral defect images. The optimized OTSU (Otsu Image Segmentation Algorithm) is used to analyze and compare the images. A defect measurement system of optical elements is developed, and color defect images are obtained upon white-light illumination. The experimental and analytical results show that single spectral or composing multispectral images from different wavelength combinations detect more defects accurately and efficiently. In the composite image, the number of detected defects increases by 1.85 times, and the area of detected defects increases by approximately 6.0 times for different kinds of defects compared to the original white-light image. The composing images from optimized wavelength combinations can be used to detect and obtain different small defects with high efficiency and high quality.