Abstract: The county in China has a relative independence and integrity，and its research can better reflect the patterns and features of regional urbanization development and process.  According to the resource endowments，socio-economic development，population status in different areas of Gansu Province，China，and taking county as the basic unit，this paper deals with the imbalances in levels and speed of urbanization development among the different regions.  Using the natural breakpoint grading method in the ArcGIS software，it can be found that the county urbanization evolution of the various regions is different. The disparities connected with urbanization are huge between the western and the eastern of Gansu.  The highlight regions of urbanization process in the central region belong to Lanzhou and Baiyin City，while the urbanization development in its other region is inferior. The paper builds up a level of urbanization development indicators，including four aspects: spatial concentration of population，economic growth，social development，infrastructure construction，and analyzes Gansu province regional disparities of county urbanization by the coefficients of variation，Williamson coefficient，maximum and minimum coefficient. Overall，the urbanization internal differences of the regions with high urbanization levels are larger，and urbanization internal differences of the regions with low urbanization levels are smaller.  The urbanization levels of the counties in the southern region were significantly lower than that in the northern region.  The core content and innovation of this paper is using geographic detector model to explore the real mechanisms of different regions’ disparities in the urbanization development from the external representation of the urbanization levels index. The different regions are affected by the different factors’ contribution in the urbanization process.  The social-economic development is the mainly effective factor to promote the urbanization of the Hexi region，improved living condition and accelerating urbanization process，but in recent years its growth rate slowing down; the central region gets relatively high score dew to the various elements，including population increase，economic and social development and infrastructure construction. The southern region is an ethnic living area，the impact of the various elements is smaller and the urbanization is slow.  The Longnan region increases in the proportion of tertiary industry and urbanization process accelerates.  The Longdong region’s urbanization is greatly affected by the constructions of energy resource and chemical industry bases and highway. Based on the models of development in the different regions three proposals are put forward: the Hexi region should focus on urban agglomeration development to drive the surrounding county to accelerate the development，thus narrowing the regional internal difference.  The southern region should increase government fiscal，financial support capabilities to provide adequate and long-term stable funding premise for county urbanization in the ethnic minority areas. The Longdong area should adopt a development model that is driven by the development of the central city，while the development of the surrounding county realizes the coordinated development of central cities and small towns.

Key words: county urbanization, geographical features, formation mechanisms, Gansu Province