Abstract: Sanxi area contains the Hexi corridor and the middle part of Gansu province and the south mountainous areaof Ningxia Hui Autonomous Region- In Hexi corrido, because there are sufficient artificial water from QilianMountains, rich sunlight and heat, the oasis agriculture is well developed, but the regional development is restricted by the limited water resource and severe desert. In the middle part of Gansu province and the southmountainous area of Ningxia Muslim Autonomous Region, vegetation is thin and soil erosion is serious and thepoverty is well known in China.
For assessing regional sustainable development planning in Sanxi area, the paper puts forward the evaluationindicator system for regional sustainable development, and it consists of three layers. Based on the evaluating indicator system, using Fuzzy mathematics method, an integrated evaluation model of regional sustainable development is estaltished and it is consisted of three sub models. The first sub model is based on the third layer of indi-cators, the second sub model on the second layer of sets of indicators, and the third sub-model on the first layerof sets of indicators. By using the model, each county, district or city in Sanxi area is evaluated. The conclusions can support the regional sustainable development plamning in the area. In the model the value of membership represents the level of the regional sustainable development. The larger the value, the higher the level of regional sustainable development is. According to the value of membership, the evaluation results is divided intothree grades : (1) the value of membership between the range from 0.6 to l represents a higher level of regionalsustainable development. (2) The value within the range from 0.4 to 0.6 indicates that the level of regional sus-tainable development is not so high- (3) The value within the range from O 0 to 0.4 shows that the region is undeveloped. Among the forty seven regions (county, city, district), there are l 3 regions with the value of membership larger than 0.6, accounting for 27. 66 percent of all the regions. mainly distributed in the Hexi CorridorArea. Eleven regions with the value of membership between 0.4 and 0.6, accounting for 48. 94 percent of allthe regions, largely distributed in Hexi Corridor Area, Dingxi Area and Hegu Area. There are eleven other regions with the value of membership smaller than 0.4, accounting for 23.4 percent of all the regions, mainly dis-tributed in Dingxi Area of Gansu Province and Xihaigu Area of Ningxia Province.

Key words: Sanxi area, Sustainable development, Evaluation, Model