Water and material balances,a conceptual model is employed to predict the situation of groundwater in urban area of Datong, Shanxi province,over a thirty-year period. With the simulation results,the main cause of groundwater deterioration can be attributed to the formation of drawdown cone due to excess draft,excess sewage irrigation and erroneous zero-outflow policy for groundwater.The concept proposed and its results may serve as scientifically based on evidence for those who are recognizing the nature of the problem of groundwater pollution,and are working to protect their local groundwater quality.