Abstract: Based on the 20-year observation data of groundwater table depth in the Yarkant River basin plain oasis from 1993 to 2012, this paper analyzes its intra-annual variations and inter-annual trends and reveals the effects of natural conditions and human activities on the variations. We calculated anomalies in these observed series to remove the influence of absent and abnormal values in the raw data, compared the changes in the whole oasis and its three sub-regions to reveal spatial variability, and analyzed the causes for the changes in groundwater table depth. Results show that during these two decades, the average groundwater table depth over this oasis was increasing significantly, and the location of peak increasing rate was moving from the middle and lower reaches to the upper one. A continual increase in the middle and lower reaches in the first decade was possibly caused by the increasing irrigation area. A continual increase over the upper reach in 2005-2012 was relevant to the canal system rehabilitation, while a decrease over the lower reach in 2003-2012 was related with the increase in water delivery through the river channel. This study has found out that human activities play an important role in spatial changes of groundwater depth and ecosystem of plain oasis.