KDP crystals with different concentrations of H 3BO 3 in solution were grown. Light scatter was detected with ultramicroscopic method. It has been proven that light scattering in KDP crystal aggravates with the increasing concentration of H 3BO 3 in the growth solution. The light loss and the transmittance characteristics were measured in KDP crystals. The experimental results show that the characteristics of light uniformity and wave plate effect greatly depend on the concentrations of H 3BO 3 in solution.