Abstract: The portable chlorine residual colorimeter was used for rapid determination of free chlorine residual in drinking water.The colorimeter was calibrated on site and the detection conditions were optimized.The result showed that the optimal temperature was 20 ℃,and the pH value was between 6-7.The interference of manganese,chromium and other metal ions could be eliminated by adding potassium iodide solution.The results showed no significant difference comparing with the standard method GB 5749-2006.