Abstract: The essence of sustainable development is to optimize the relationship between man and nature and between man and man.Although the supporting capacity of environment for human population is limited, the sustainability of human ecosystem can be realized through cultural adjustment.Such system properties as productivity, stability, resilience,equitability, autonomy and harmony can be used to identify the sustainability of human ecosystem.According to these principles, the approaches to optimize man-earthsystem are to control human demands within the carrying capacity of the system ito make the natural resources reproduction socialization.to equilibrate the demand and supply of natural resources by means of price mechanism, and to bring government intervention and public participation into play.

Key words: Human system, Sustainability, System properties, Cultural adjustment, Optimization approaches, organic nitrogen, distribution, influence factors, inorganic nitrogen, zonal soils