Henan Coal Mine is a large water mining area in China, and the groundwater in the goaf area is serious. Through the comprehensive analysis of the water chemical environment, water chemical characteristics and water chemical causes of acid old kiln in coal mines in Henan Province, the principle of treating acid water in mines by chemical desulfurization technology and the use of synthetic coagulant were proposed, and the corresponding process parameters were derived. That is, the weight ratio of calcium hydroxide and tetracalcium ferroaluminate in the synthetic coagulant is 1:1.3~1:1.5; The quicklime input can be appropriately reduced by 10 mg/L for every 50 °C increase in the water temperature of acid old kiln. For each unit increase in pH value, the quicklime dosage decreases by 25 mg/L. Practice has proved that it is feasible to treat mine water with the above physicochemical methods and process parameters.