COD is the important index in the inspection of water quality,its measurement include the method of K2Cr2O7,and the sealed digestion method etc.But all these methods have some problems.This paper major presents a method of determining COD by the opened tube.On the basis of the standard determination of COD using potassium dichromate as oxidant,the opened tube digest——visible light spectrophotometer in the existence of recombination catalyst has been applied to the determination of COD in the serial standard...