Niangziguan spring as the main source of water supply to Yangquan City is affected by the particular geological structure and human factors such as water pollution， deteriorating trend and component content exceeding the standard. This paper evaluated the effect of the river seepage on the pollution of the water quality of the Niangziguan spring with the physical mixing method by analyzing the karst water system on the basis of geological structure， and making observation and measurement of the main river leakage and water chemistry.