KDP crystals with different concentrations of EDTA in solution were grown. Light scatter was detected with ultramicroscopic method. It has been proven that light scatter in KDP crystal aggravates with the increasing concentration of EDTA in the growth solution. The increase with light scatter occurs since EDTA inhibits the growth of KDP crystal at high concentration, which results in the formation of mother liquid inclusions, which in turn causes light scatter. The density, size and shape of light scatter are varied within different sectors of the KDP crystal. The mechanism of the effect is discussed.