Ejin River, also Etsin Gol, Ruo Shui or Ruo He in ancient times, is a major river system of northern China. It flows approximately 630 kilometres (390 mi) from its headwaters on the northern Gansu side of the Qilian Mountains north-northeast into the endorheic Ejin Basin in the Gobi Desert. The river forms one of the largest inland deltas or alluvial fans in the world. Its drainage basin covers about 78,600 square kilometres (30,300 sq mi) in parts of the Chinese provinces of Gansu and Inner Mongolia, which flows within the Zhangye area of Gansu; when it flows across Jiuquan area, it was renamed as Ruo Shui; when it flows across Alxa League, it is called Ejin River.

The Qilian Mountains, together with the Altyn-Tagh also known as Nan Shan, as it is to the south of Hexi Corridor, is a northern outlier of the Kunlun Mountains, forming the border between Qinghai and the Gansu provinces of northern China.