Land degradation is widely distributed in China, mostly in arid and semi-arid areas. Identifying which ecosystem types can be achieved through ecological restoration processes is key to ecological restoration success. This is the research focus of ecology subject. Taking the Helin County of Inner Mongolia, located in the semi-arid area of northern China, as an example, this article explores the method to identify key ecosystems through ecological functional zone planning, accompanied with an analysis of existing vegetation surveys, climate change and national vegetation regionalization. By integrating methods of document collecting, field surveys and 3S technology, based on analysis of eco-sensitivity and eco-services, Helin County is classified into three eco-regions, and 11 sub eco-regions. The eco-regions are decided by topographic features, and the role which Helin County plays in the national ecological function regionalization of China. In the national ecological function regionalization, the ecosystem services in Helin County are soil conservation (in most areas), agricultural products supply, and mountain water-source conservation (in small areas). The ecological score of how precipitation, slope degree, slope aspect, soil texture and vegetation index contribute to soil erosion sensitivity in the region is calculated and the sum of these values with different weights is regarded as the value of soil erosion ecological sensitivity. The contribution of drought index, soil type, drought index after 50 and 100 years, and vegetation cover to land desertification also are quantified and summed into values of land desertification ecological sensitivity. Then a value for protection importance of the ecosystem is calculated, and a value for water supply is calculated through hydrologic analysis. The sub eco-region is formed by the ecological sensitivity of soil erosion and land desertification, the protected value of ecosystem, and the function of water supply. Areas with the same ecological value and ecological problems are put into the same sub eco-region. On the basis of the main ecosystem service function of every sub eco-region, the possible ecosystem type which produces such functions can be deduced. The vegetation types of Helin County were classified according to the Vegetation Zoning of China, a vegetation zoning map considering climate, soil and water factors, and were used for the deduction of key vegetation ecosystems. Vegetation ecosystems existing in the national vegetation zoning classification should be restored. The locations of ecological restoration should be limited to areas in which the vegetation ecosystem is different to the key ecosystem. The vegetation change under climate change is also simulated. An ecosystem that is different from the key ecosystem should not be included in ecological restoration if it will be the same as a key ecosystem after 50 or 100 years. Compared with existing vegetation identified by field surveys, where ecosystems are obviously different from the key ecosystem, they should be restored. With these steps, the potential key vegetation ecosystems can be identified.