Abstract: The wastewater is digested in domestic microwave oven (Model:Galanz-WP900)to determine its chemical oxygen demand(COD).Compared whth standard method,less time,energy and reagent are required in the air-proof microwave digestion.Ag₂SO₄ and Hg₂SO₄ are no longer neccessay as catalyst and screening agent,which help avoid secondary pollution.For different range of COD_Cr,the determination results were better under proper concentration of chlorion,and the method is very suitable for determination of a batch of samples and/of continuous monitor.The research results show that the method has better accuracy at determining the COD_Cr and obtains similar results with the standard method of COD_Cr of determination.