Shaya County is located in the upper reaches of the main stream of the Tarim River. As one of the typical agricultural areas, its crop growth water source mainly comes from watershed irrigation. Studying the temporal and spatial changes of crop land not only helps to monitor agricultural land in the region and analyzes agricultural water consumption to provide a decision to rationally allocate water resources in the Tarim River, but also can help to monitor illegal land reclamation. This paper selected 94 medium resolution images of Landsat 5 TM and Landsat 8 OLI from 1994 to 2018, and used the socio-economic statistical yearbook in the corresponding year, hydrological data and Populus euphratica distribution data, combined with the main crop phenological information in the study area, based on multi-time remote sensing images, the information of the sown area of crops in Shaya County was extracted and the temporal and spatial dynamics were studied. And the reasons for the change of planting area from the aspects of water resources and the relationship between cultivated land and Populus euphratica forest were analyzed. The results showed that: 1) The main crops in Shaya County were cotton, wheat and corn. The usage of multi-temporal data to extract the planting area of crops according to their different phenological laws could not only greatly improve the accuracy of the extraction result of the sown areas of crops, but also avoid the leakage phenomenon caused by different growth periods of major crops, and it could be used to improve the extraction precision of the whole crop planting area by using the complementarity between the various time images; 2) The crop planting area in Shaya County showed an increasing trend in 1994-2018, especially showed a rapid growth (2006-2018) after continuous slow growth(1994-2006), and the two periods with larger increase rates were 1994-2006 and 2008-2011; 3) The planting area of the Weigan River Irrigation District had a spatial trend from the inside to the outside, from the fragmentation to the centralized contiguous development, the increased area was distributed in the eastern and southwestern parts, while the area of the sown area of crops in the Tarim River Basin had increased along the main stream of the Tarim River, and its increased area was mainly distributed on the south bank of the upper reaches of the Xinquman Station on the Tarim River and its downstream north bank; 4) The increase of crop planting area in the Weigan River irrigation area had a strong correlation with the change of the inflow water volume in the upper reaches of the Weigan River, with a correlation coefficient of 0.89, while the area in the main stream of the Tarim River had a relatively low correlation, with a correlation coefficient of only 0.31; 5) The Populus euphratica forest area in the main stream of the Tarim River was cultivated every year. The area occupied by encroachment showed a growing trend, although the protection measures for Populus euphratica forests continued to strengthen after 2006, The planting area of crops showed a trend of accelerating growth after 2008, and the phenomenon that the invaded Populus euphratica forest failed to recover and the new Populus euphratica forest was destroyed.