In this paper the worldwide geographical distribution of the genus Achnatherum is discussed in detail．The paper is divided into following five parts：1．Conspectus of taxonomic system：The genus Achnatherum Beauv．comprises 23 species，which can be grouped into 5 sections．The characteristics of each section are described．An infrageneric system including species in each section is presented．2．Geographical distribution of the genus：The northernmost occurrence of the genus is represented by A．sibiricum and A．confusum at latitude 62°N and the southernmost by A．chingii var．laxum at latitude 26°N．As far as vertical distribution is concerned，the lowermost record of latitude in the genus is at 120 m (represented by A．bromoides)and the highest record at 4600 m(by A．jacquemontii and  A．duthiei)．3．Systematic position and geographical distribution of sections：The systematic position of five sections in the genus，i．e．，Sect．Achnatherum，Sect. Timouria，Sect． Aristella，Sect．Neotrinia and Sect．Achnatheropsis，species in each section，and the distribution pattern of each section are discussed．4．Geographical distribution of species：According to Takhtajan‘s regionalization of the world flora，the number of species in each region is presented．The Irano—Turanian Region(18／24)comes to the first in number of species，followed by the Eastern Asian Region(14／24)．Seventeen species have been found in China， where the Hengduan Mountain Region，Huabei Region and Tangut Region are the richest in species(10 species and 9 species，respectively)．5．Discussions and conclusions：(A)The analysis of distribution patterns of species shows that the centre of distribution of Achnatherum．is located in the boundering area of the Hengduan Mountain Region，Tangut Region and the Huabei Region．  (B)Based on the analysis of evolutionary trends in morphological characters of Achnatherum and geological evidence, it is presumed that this genus probably originated in north part of the Hengduan Mountain Region. (C) Three migration routes lead to the present distribution pattern:a) From the Hengduan Mountain westward along the Himalayas across Kashmir Region to the Mediterranean and Central Europe. b) From Hengduan Mountain northward across the Qilian Mountain, west of the Huanghe corridor, Tianshan Mountain, mountains west of the Tarim basin to the Issyk lake. c) From Hengduan Mountains northeastwards across Gansu, Ningxia, Shaanxi, Hebei, and northeast part of China to Siberia, eastwards to Kamchatka Peninsula, westwards to upper stream of the Ob River, and across the Asia-Bering Land Bridge to Nevada and Rocky Mountains in west United States. (D) The majority of species of Achnatherum are distributed in subhumid, semi-arid and arid areas,and also on mountains of extremely arid desert region in the Northern Hemisphere. A series of morphological- ecological characteristics of mesophytes and moderate xerophytes and life-form resulted from long-term adaptation and evolution.