Alashan desert, sited in the east of Asia desert, is a special vegetation geography area in Asia desert region. Its geographic range is from west Ordos (108 degrees E) to west Ejina (98 degrees E), and from Gobi-Altai Mountain in Mongolia (43 degrees N) to Hexi Corridor (37 degrees-39 degrees N). The annual plants grow well, and are constant synusiae that act on important function in keeping the stabilization of desert ecosystem in Alashan desert. Moreover, the annual synusiae may take on heavy responsibilities in local animal husbandry production. The specific diversity and distribution characteristics of annual synusiae are discussed in the paper. Based on our observation and research in many years, 61 species of annual plants, which could be divided into 4 types of annual short grass, annual Salsola, annual Artemisia and annual weeds, are discovered in Alanshan desert. They belong to 12 families and 35 genera, and could be divided into 12 areal types, and 10 species of them were endemic to Alashan. The annual plants grow widely on clayey deserts, sandy deserts, gritty deserts, gravelly deserts rocky deserts and oasis. In general, one or several plant species form summer rain synusiae, and form a homogeneous or patchy distribution pattern in desert communities. Sometimes, some plant species distribute along runoff line, and form a dendritic or line pattern. The ecological adaptation and function were also discussed in the paper.