Abstract: Pinus yunnanensis stand system is an open system for exchanging matter and energy with outside environment to form a unblance state, stable and order saturated stand structure through asynchronous growth of its daughter systems which consist of upper story dominated trees and understory suppressed trees.In the saturated stand system, the numbers of suppressed tree differentiate from dominated trees each year and the death amount of suppressed tree are coordinate so as to maintain its structure which could contain dominated tree 30-40%,and its volume 60-70%.In order to make stands return into saturated stand system structure, the growth increment of dominated tree should be increased by thinning Ⅲ, Ⅳ, Ⅴ class tree; and the amount of suppressed tree death should be decreased simultaneously.The daughter systems of dominated trees evolve differently with the whole stand system, as a result of stand system density which is memerical assemble determined by interaction of site quality, age and density, which evolve according to the curve locus of the power function, its coefficient "A" increasing with the reduce of stand density, and the value of "B" decreasing with the reduce of stand density. The evolution law of stand system for Pinus yunnanensis has the practical values for the predicting reserved amount of dominat tree and determining the thinning intensity.

Key words: Pinus yunnanensis stand system, Formation, Evolution