Building a swimming pool water circulation system to simulate on-site residual chlorine monitoring.Comparison of the results from the constant voltage chlorine sensor,diaphragm chlorine sen-sor,and analyzer of DPD photometry is carried out based on the test results from HACH detector,to find the most suitable analyzer for online monitoring of residual chlorine in swimming pool water.And researc-hing on the factors that lead to differences in test results from three analyzers.The results show that the analyzer of DPD photometry which is most suitable for online monitoring of residual chlorine in swimming pool water performs the best in terms of test accuracy and stability.The combined chlorine in swimming pool water caused higher test results from constant voltage chlorine sensor,and high turbidity of water caused more poor stability of diaphragm chlorine sensor.