The frequent accidental water pollutions in China have brought serious environmental pollution and economic losses. These accidents were largely caused by the relevant personnel's serious lack of the recognition of damages and trends of sudden pollutions, inadequate emergency preparation and delayed emergency response. According to the law of pollutants diffusion in water and dynamic development tendency of ecological damages and pollution-control cost, the study established the decision-making model which chose the emergency response time as the decision variable. The objective function of the model was the total cost of emergency treatment. The study chose water standard and emergency supplies preparedness time as constraint conditions and quantitatively evaluated the effect of the time for procuring, loading, transporting, unloading and assembling emergency supplies on the object function by the scenario analysis method. The model revealed the influence degree of the emergency supplies preparedness time and field conditions on the total cost of emergency treatment. The emergency pollution-control cost will increase by about 1.63 million RMB when the emergency response was delayed by 1 hour in the hypothetical typical sudden water pollution. The research results not only showed serious consequences caused by the delayed emergency response but also provided decision-makers with quantitative information support in the aspects of selecting strategic points and technical programs of emergency treatment and establishing the emergency supplies depository.