Abstrat Small watershed is a complexed system of ecology and economy,of which the ecological system has exchange of energy,material and information with the external and could absorb negative flow of entropy,which makes the system leave balanced stable and tend to the ordered structure of the economy system man power and natural resource play predominant effects on the complexed system of ecology and economy,it is thought that to coordinate the relationship between human activity in society and economy,it is thought that to coordinate the relationship between human activity in society and economy and the economy,it is though that to coordinate the relationship between human activity in socitety and ecology and economy,it is thought that to coordinate the relationshio between human activity in society and economy and the ecological system is the fundamental problem for the harness of small watershed.Only when approaching from the factors of nature and social economy and their regineering like dynamic simulation of system and ecological principle,and finding the key problems in the system through a series of logical and nathematical analysis,might it be possible to design harness plan and dispoes the measures.It is said that the ultimate goal to harness small watershed is to establish a stable,enduring and effcient system of ecology and economy