Abstract: Agreat number or historical racts snow that man's mnuence to ecosystem has become stronger and stronger and has gradully held on a certain special niche. According to the ideas of "progressive centralization" and "progressive mechanization" in L. v. Bertalan ffy's General System Theory,by reasoning the evolutionaiy process of cell and indivi dual from analogy,man's niche in ecoystem is deduced: it is not only the linkage of food chain,but also the regular-controller in ecosystem. On the basis of classical ecology,fully considering man's niche,a four-unitary structure of ecosystem including producer,consumer,decomposer and regular-controller is put forward. Further analysis shows that the appearance of mankind is the necessary historic product in the evolutionary process of ecosystem; social-economic-natural ecosystem is a two levels structured system with man kind as a contre and has a complex mechanism.

Key words: Mankind, Niche, Regular-controller