Abstract: Resource and environment carrying capacity and suitability evaluation of territorial space development are the basis of territorial space planning. The county-level territorial space planning plays a role of linking the preceding and the following, so “double evaluation” is the key issue of how to support the county-level territorial space layout. The authors in this paper took Qingxu County of Shanxi Province as the research area, and focused on four key issues, including the selection of resource and environment elements, suitability evaluation of territorial spatial development, resource-environment carrying capacity evaluation, and optimization of territorial space planning. The territorial space optimization model was proposed based on the resource and environment elements analysis by short-board and long-board theory and the regional characteristics plus up-down coordination. Besides, the county-level “double evaluation” framework system adapted to regional characteristics was constructed. The results show that Qingxu County is basically a suitable area for agricultural production and urban construction, except for the western mountainous area and both sides of Fenhe River, which are extremely important areas for ecological protection. The scale of agricultural production and urban construction in Qingxu County is mainly restricted by water resources, and some agricaltural irrigation areas in this region have already exceeded their water resources carrying capacity. The priority development areas of Qingxu County's ecological, agricultural and urban development were reasonably divided. Meanwhile, suggestions for the optimization of county-level ecological space, agricultural space and urban space were put forward, which could provide some basic support for the detailed layout of county-level territorial space in Qingxu County.