Automatic control device according to the proportion of flow changes measured by flow detection device, automatic control of sodium chlorite and hydrochloric acid dosage to achieve the appropriate CLO2 production. Sodium chlorite (NaCLO2) and hydrochloric acid (HCL) reacted to generate high yields of high-purity CLO2 disinfectant. ★ can be adjusted according to the amount of water changes CLO2 automatic dosage, without staff on duty, so economical and efficient. Particularly suitable for high-rise building water supply, owned wells, swimming pool water, water reuse, wastewater disinfection hospital.