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.

[2] Parts of the river flow through the Hexi Corridor, a valley which once formed a significant portion of the Silk Road.

Many outposts were created to protect Silk Road traders from the frequent attacks of barbarians, as the water-abundant valley of the river in relation with the aridity of the surrounding terrain provided an easy route for Huns and Mongols to launch raids.

However, clearing of the landscape has caused increased erosion, leading to desertification of the region and a gradual reduction of the river flow.

The loamy sediment load gives the waters a dark colour which, during time, has contributed to the river being described as Hei (黑), that is Black.

Most of the precipitation fallen annually over the basin is concentrated in this area, creating two main river courses that join just north of the hydrometric station of Yingluo.

The midstream area is characterized by the presence of wide ranges of cultivated fields, mainly in the oases that follow the principal route of the river.

After the stream gauge at Zhengyi, the river describes a wide north-east turn, developing its last 400 km in the western fringe of the Badain Jaran Desert.

Because the climate of the area has followed a drying trend over the past 10,000 years or so, the delta is no longer considered active (i.e. deposits are not being built up significantly) and is slowly being eroded by wind and water action.

term, when shifting from the vegetated (upstream and midstream) to the arid (downstream) areas, the transpiration element decreases in importance in favour of the simple evaporation.

This flow weakening is the result of the net balance between the tributaries descending from the north-east side of the Qilian Shan and the considerable derivations related to the cropfield area.