In view of the existing problems of high analysis cost, long time and easy to make two pollution during determining COD by the national standard detection method,dichromate method. The test of these methos which are rapid digestion spectrophotometric method, oven method and COD rapid was carried out to find a fast COD method for the wastewater treatment of a sewage treatment plant. The results show that the fast digestion spectrophotometry overcomes the shortcomings of the national standard method and obtains the COD monitoring result equivalent to the national standard 2 h reflux method.