Online residual chlorine electrode consists of cathode and anode,cathode is gold electrode,anode is silver/silver chloride electrode,cathode and anode are immersed in electrolyte chamber filled with electrolyte,through film and measurement environment isolation,film can prevent electrolyte leakage or contaminant infiltration,but hypochlorous acid can pass through the film,the measured hypochlorous acid concentration and the measured current proportional relationship,through pH compensation,to obtain the residual chlorine concentration.