Abstract: In contrast with eastern developed cities，revealing the spatial pattern and evolutional characteristics of population in western under-developed cities means a lot. It is also conducive to understanding the urban population distribution pattern and guiding it in an orderly way. Based on the spatialization of population data at township and street level, with the methods of deformed elliptical circle, GIS spatial analysis, population density model and so on, this paper revealed the spatial pattern and evolutional characteristics of population in Lanzhou during 2000-2010. The results show:①The population density distribution of Lanzhou showed “band agglomeration” feature and “circle-difference” structure, forming a pattern of “the population grew slowly in central region and inner suburbs, grew rapidly in peripheral region, and reduced significantly in outer suburbs”. ②The population center of gravity moved towards north-east during the ten years. And the population spatial distribution showed “northwest-southeast” pattern, representing agglomeration trends, which was strengthened during the ten years. ③Smeed model was the best single-center model to describe the population distribution of Lanzhou. The single-center trends of population distribution strengthened during the ten years, while the population polycentric structure was not in evidence.