Based on the chemical test data of groundwater in the oasis area of Hotan River Basin, Xinjiang in 1980, 2014 and 2017, the single index evaluation method was used to evaluate the groundwater quality and identify the key influencing indicators. Meanwhile, the spatio-temporal evolution characteristics of groundwater quality in this area was analyzed. The results show that the quality of unconfined groundwater in the oasis area was generally poor. In 1980, 61.8% of groundwater was classified as IV and V, 91.1% of groundwater was classified as IV and V in 2014, class IV and V water accounted for 71.0% in 2017. In addition to the major components (such as TDS, TH, Cl-, Na+ and SO42-), the key indicators affecting groundwater quality also included trace components such as F-, Fe, Mn and BaP. In the horizontal direction, the distribution law of groundwater quality in the oasis area in 1980 and 2017 was similar, and the groundwater quality in the middle and upper part of the alluvial-diluvial plain, especially in the area affected by river seepage at the mountain pass was better, whereas that at the end of alluvial-diluvial plain was poor. In 2014, the distribution area of class V water was the largest, whereas class III and IV water were scattered. In the vertical direction, the quality of shallow groundwater was generally inferior to that of middle and deep groundwater. The quality of groundwater in the oasis area decreased gradually from 1980 to 2014, and then showed a slightly improving trend from 2014 to 2017.