Abstract: The growth regularity of Pinus yunnanensis natural secondary forest stand in Yipinglang forest farm was studied, basing on the stem analysis data, with the methods of standard plot and stem analysis. Six theoretical equations :a power function type , parabolic type , logistic type , logarithmic curve type, michael schumacher type were used to established the growth model systems of average tree and dominant tree with MATLAB statistic software. Then the optimal mathematical growth models were chosen by regression analysis. The results showed that : the fitting precision of the optimal mathematical growth models between 96. 67% and 98. 97%. It was thus clear that the predicting effects of these models had good ftting precision and adaptabilty for the tree growth process ,so they could be used to predict the study area of Pinus yunnanensis natural secondary forest growth process There are two fast-growing period of average tree and dominant tree, which as 5- 10 years and 35 - 40 years. Proper intermediate cutting was suggested during the age of 10 -15 years ,40 -45 years ,so as to promote the fast growth of stand. . The current annual volume increment curve and mean annual volume increment curve didn’t meet in the 50 years, indicating that the forest didn't reach its quantitative maturity age , and its quantitative maturity stage was after 50 years. In the 50 years,the total volume increment and the current annual volume increment of the dominant tree are 4 and 5 times more than that of the average tree ,showing strong beneficial in artificial selection.

Key words: Pinus yynnanens is, Natural secondary forest, Growing rule