Keywords: 
• groundwater chemistry environment /
• chemistry simulation /
• water-rock reaction

Abstract: Based on the systematic study on the groundwater chemistry typer and their evolutional characteristics in the Shiyang river basin, the author hasthe evolution mechanism of chemical environment of the groundwater in the Shiyang river basin by the saturation index (SI) obtained through chemical simulation program. Some cognitions are reached as follows: 1. Groundwater chemistry types of the Shiyang river basin show the complete zonation, i. e, bicarbonate zone is mainly distributed in the mountainous fissure water in the upper reach and mountain front gravel area; sulfate zone is in the mountain front alluvial and fluvial plain in the middle reach; and chloride zone is in the desert and salt depression area in the lower reach. 2. In April (dry period), the calcite and dolomite are oversaturated both in the upperreach (Wuwei basin) and the lower reach(Minqing basin), but in August (rain period) the SI of the calcite and dolomite decreased obviously in Wuwei basin. In the meantime that in Minqin basin had an obviously increasing trend and both calcite and dolomite reached over saturation, implying that groundwater chemistry environment in the lower reach of the Shiyang river basin is mainly controlled by evaporation. 3. Groundwater overdraft in recent ten years has resulted in the chemistry types of the groundwater changed from bicarbonate to sulfate and even chloride in the lower reach, especially in the margin area of the desert, showing the increasing trend of mineralization and worse groundwater quality.