Recent geo-researches display two significant features. First, most research projects are centered on revealing the implications for regional sustainable development and ecological security; and second, these projects try to employ an integrated approach to taking both physical and socio-economic factors into consideration. Indeed, the implementation of sustainable development strategy demands a classification of territorial systems based on such an integrated approach. To be integrated, a key scientific issue is how to synthesize the physical and socio-economic factors in the process of classification. Based on a new indicator system, which involves mainly physical indicators at the macro level and socio-economic indicators at micro level while employing both at the middle level, this paper tries to develop a new integrated approach to the classification of territorial systems to reveal the features of human-nature relationship at various spatial levels. The new system of classification is a hierarchy consisting of five levels: class zero realm; class one ecological zone (and/or) sub-zone; class two land-human region; class three eco-economic division; and class four economic districts. The classification at the first three levels is a "top-down" process; that at the fifth level is a "bottom-up" process; and that at the fourth level is a matching process from both the top and the bottom. The paper further tests the new approach of classification via a case study of the Tibetan Plateau. By the approach, the Plateau is divided into 3 zones, 15 regions, 22 divisions and 29 districts. Such classification results have profound implications for regional sustainable development.