Abstract: The Mosowan District is situated in the southwestern part of the Junggar Basin. It is covered mainly with fixed and semi-fixed sand and sand dunes, and is part of the vast Gurbantunggut Sandy Desert. With a typically temperate desert climate, the dominant vegetation hece is temperate dwarf semiarbor communities.Though the climate is severely continental, yet the ephemerals develop rather well because of the following reasons: 1) In spite of scarcity of annual rainfall, there is a certain amount of accumulated winter snow and spring rainfall, which provide the ephemerals with favourable moisture. 2)The substrate consists of loose sand which, with weak capillarity, can keep to some extent moisture from evaporation during the dry period of the year. From spring to early summer, the ephemerals with their shallow root systems can sufficiently use the water of the moist sand substrate. 3) Though winter is severe and summer is very hot, yet spring is mild, and heat is enough for their highly efficient photosynthetic system to work, and the great daily temperate rang(, is favourable for the accumulation of photosynthetic products.42 species of ephemerals have been recorded in the Mosowan District. They belong to 38 genera and 16 families. Ephemerals in the Mosowan District are important members of the two communities of Haloxyneta. Their great coverage and biomass make them important in the spring production structure. They form special spring synusiae of communities. Besides, they occur usually as conglomerates on the bare substrate and constitute the pioneer stage of community development.