It is very urgent to solve the problem of electrolytic efficiency of chlorine evolution in extremely dilute chlorine-containing solution for the electrochemical advanced oxidation process, electrochemical antifouling and chlorine-containing disinfectant preparation. In this paper, the IrO2-Ta2O5 electrode is modified by SnOx, and the activity and selectivity of chlorine evolution reaction (CER) are successfully improved. The modification of SnOx changes the electronic structure of IrO2-Ta2O5, thus affecting the electrochemical reaction process and mechanism. Compared with those of IrO2-Ta2O5 electrode, the CER activity of SnOx@IrO2-Ta2O5 electrode is increased, while the OER activity is decreased. At a current density of 50 mA cm-2, the potential difference between CER and OER of the SnOx@IrO2-Ta2O5-3 electrode is 254 mV, which is 89 mV higher than that of the IrO2-Ta2O5 electrode. This proves that the selectivity of CER at the SnOx@IrO2-Ta2O5 electrode has been improved. Due to the low concentration of chloride ion, the current efficiency of IrO2-Ta2O5 electrode is only 10.7%. The current efficiency of SnOx@IrO2-Ta2O5-1(2,3) electrode increases to 23.6%, 36.7% and 49.6% respectively. For the IrO2-Ta2O5 electrode, its rate-determining step (RDS) is the second electron transfer. However, for the SnOx@IrO2-Ta2O5-3 electrode, its RDS is the electrochemical desorption. It can be inferred that the modification of SnOx can accelerate the electrochemical desorption of adsorbed Cl. In addition, that application of SnOx@IrO2-Ta2O5 electrode in the preparation of AEW is investigate. The HClO of AEW2 (prepared by SnOx@IrO2-Ta2O5-3 electrode) is 1.85 mmol L-1, which is 4.6 times that of AEW1 (prepared by IrO2-Ta2O5 electrode).