This paper established the assessment system at county-level for Gansu Province, which included 1 target, 3 norm and 19 index levels. The scores of ecological, economical and social factors in 87 counties of Gansu Province were calculated based on PCA method and SPSS software, and the map of regional sustainable development （RSD）of Gansu Province was obtained based on GIS. The results showed that: the spatial difference of RSD level was obvious at county-level of Gansu Province. Generally, RSD level was higher in the east and south areas than in the west and north areas. The highest RSD level appeared in Lanzhou and Hezuo while the lowest of RSD level in Anding. RSD level was lower in Hexi while it was middle in the central arid and semi-arid areas. The above results were agreed with the actual situation of Gansu Province, which proved the high reliability of the established assessment system. Finally, some proposals were given in the paper on the RSD of Gansu Province.