Abstract: Based on the huge chemical analysis data of the produced water gathered from the CBM wells in Zaoyuan block, Qinshui basin, the change of chloride ion concentration with time was investigated by statistical methods. The results show that the chloride ion concentration far exceeds the class drinking water Ⅱ standards in the early drainage stage. Therefore, the produced water has the biggest influence on the environments in the early drainage stage. A mathematical model is established by nonlinear regression analysis using SPSS. This model can well forecast the time needed for the water to reach the state's standards. Hence, it can provide technical support for the CBM produced water quality monitoring and treatement on ground.