Abstract: The small white spot defect was found on the surface of B50A800 non-oriented silicon steel plate produced by a company during the production. The formation reasons of the defect were analyzed by macro analysis, chemical composition analysis, hardness test, scanning electron microscope and energy spectrum analysis and so on. The results show that element sodium was introduced due to the incomplete cleaning during the water cleaning section, and element chromium was introduced due to the incomplete cleaning during the coating section. The introduced sodium element and chromium element reacted with the acid root ions in the coating liquid to form impurities which was microscopically displayed as shell-shape and macroscopically displayed as small white spots, so the small white spot defect was generated on the surface of the silicon steel plate. Finally, corresponding improvement suggestions were put forward and good results were achieved.