The present invention relates to an on-line residual chlorine sensor with a self-cleaning device, the on-line residual chlorine sensor comprises a constant current device, a T-tee, a three-way solenoid valve and a flow-through cell, the beneficial effects are as follows: 1) physical grinding and hydrochloric acid washing are performed interactively, the physical grinding strength is controllable, performance is improved, effect is better, and the on-line residual chlorine sensor is fully automatic and controllable; 2) the micro constant current device can ensure a smaller volume, meanwhile substantially increases the output end pressure, and increases the load capacity to increase the reliability of a waterway, and the constant current device rear end waterway may not cutoff; and 3) the constant current device flow rate is affected by earth gravity, liquid level difference and the water flow pipe diameter section, influence on performances are in linear relation, and analysis, debugging, testing and use are facilitated.