Variation of the major ions’ concentration in wet and dry seasons for the past more than 20 years in Maocun underground river are studied, and the water quality evolution trend is predicted on the basis of the water quality assessment. The result shows that most of ions and index accord with standards Ⅰand Ⅱ prescribed by Groundwater Quality Standard (GB/T14848—93), water quality is comparatively good. However, the ion concentration is increasing generally because of change in land use, climate and other natural conditions, and the water quality is getting worse correspondingly.