Abstract: Coating defects appeared on the surface of a certain non-oriented silicon steel plate during production. The causes of the defects were analyzed by macro observation, chemical composition analysis, hardness test, energy spectrum analysis, coating thickness test and so on. The results show that the width specification of the non-oriented silicon steel plate was changed during production. The residual non-green coatings of narrow silicon steel plate was not compatible with the green coatings on the surface of wide silicon steel plate during production. As a result, the coating defects of the non-oriented silicon steel plate were produced and the coatings were uneven.