Abstract: The food security is related to the national economic development and the social stabilization. The study on regional difference of per capita grain possession and its driving mechanism at the county level is significant to regional food security in the situation of limited arable land and rapid urbanization, especially in underdeveloped areas. Agricultural statistics of Gansu Province at county level for the period of 1991-2011 is collected and the GIS spatial analysis technique as well as other tools such as Moran��s I, Getis-Ord and gravity model are introduced to describe the spatial variation of per capita grain possession at county level. Geographically weighted regression (GWR) model was used to explore the driving factors of per capita grain possession, and the aim is to illuminate the current situation of per capita grain possession, provide the scientific basis for sustainable development of agriculture in Gansu Province, and guarantee national grain security. The conclusions are as the follows. Firstly, per capita grain possession showed an overall trend of rise but fluctuated occasionally over the period of 1991-2011. The gravity center of per capita grain possession transferred from the northwest to southeast. Secondly, per capita grain possession at county level in Gansu showed a strong positive spatial autocorrelation that the similar areas clustered in space. The regional per capita grain possession had a significant spatial-temporal variation, and the trend of speciali-zation and regionalization was enhanced. The county-level per capita grain possession had been gradually depolarized. LISA cluster map demonstrated that counties with higher per capita grain possession gathered in the middle part of Hexi Corridor, while counties with lower per capita grain possession gathered in the area of Longzhong Loess Plateau and Gannan Plateau. Spatial pattern of hot spots and cold spots changed significantly during the past 20 years. Thirdly, the driving forces of the evolvement of per capita grain possession can be identified through the following aspects: the basis of natural conditions, the policies on regional development, the interaction among economy, science and technology, and the productive factor. Effective regulation and favorable policies can promote per capita grain possession and guarantee regional grain safety. The driving factors of different regions show localization characteristic of non-stationary intercourse. The effect of population change on variation of per capita grain possession is the largest, whose coefficient estimation is negative. The secondary factor is the economic development level. The urbanization rate is the third influencing factor, and it is negatively correlated with per capita grain possession. The majority of factors that influence the per capita grain possession of Gansu at county level showed obvious latitudinal zonality or longitudinal zonality.