Abstract: Located in Junggar Basin in north Xinjiang, China, Gurbantunggut Desert, with an area of 48, 800 km², is the second largest desert in China. Fixed and semifixed dunes are the main types in the desert, and the mobile types of dunes are similar to that in some deserts in the sem-i arid areas in east China. In this paper, the formation causes of the fixed and sem-i fixed dunes are analyzed. The research results show that the fixed and sem-i fixed dunes form under a synthetic feeect of many factors, such as precipitation, snowcover in winter, suspending wet sand layer, vegetation growing in the level areas betwwn dunes and on the leeward slopes, slightly weathering on sand surface, sand granularity, etc. comparing with some deserts in east China, seasonal variation of precipitation is small in Gurbantunggut Desert. Its precipitation during the period from November to may occupies 30～55% of th total annual one, whereas it only occupies 10～25% of that during the same period in some deserts in east China. There is table snowcover in thickness of 10～25 cm in Gurbantunggut Desert in winter, and its duration varies in a range of 70～130 days. In snow melting season in spring, the thickmess of wet sand layer can be 50～60 cm, and its water content can be more than 25 g/kg in Gurbantunggut Desert. Gale blows mainly during the period from April to July, vegetation, however, grows well in the level areas betwwn sand dunes, particularly ephemeral plants swiftly grow, and the vegetation coverage is over 30% in the hinterland of the desert. In addition, soil forming process here is poor, and the content of organic matter in surface layer is higher than that in subsurface layer. Sand granularity in Gurbantunggut Desert is coarser than that in Taklamakan Desert. All and suggest that Gurbantunggut Desert is characterized by fixed and sem-i fixed dunes.

Key words: Gurbantunggut Desert, fixed and sem-i fixed dunes, formation cause