The experiment shows that it is feasible to determinate the chemical oxygen demand(COD) of the water from styrene condensate stripper by Fushun chemical plastic plant. We Compared the rapid determination method by COD tester and assay. These results show that the accuracy and precision of relative standard deviation (RSD) is between 0.0%～5.0% through the calculations of the standard addition recovery rate and the measurements of the standard sample. These results meet the requirements of the water quality monitoring in laboratory. Therefore, the above method can be promoted for application.