Abstract: Pinus yunnanensis and P.armandii are the main timber trees in southwest area of China.In order to study the relation between stand density and forest growth and manage the forests of P.yunnanensis and P.armandii well,theau-thors have made a stand density control diagram of the P.yunnanensis forest in central Yunnan and the Nanpanjiang district and that of P.armandii forest in Guangyuan on the basis of the theory and method used at home and abroad.The sample plots made through typical selection can express the growth situation of P.yunnanensis and P.armandii in these areas.Theauthors have made 493 sample plots of P.yunnanensis in central Yunnan,305 in Nanpanjian district and 252 of P.armandii in Guangyuan.This paper has elucidated not only the method of data collection and arrangement,but also the selection of the mathematical model and the drawing method of the full density curve,equal height curve,equal diameter curve,density control curve and the natural thinning curve by means of mathematical tables.The authors have tested the precisions of the diagrams in theory and practice after making them.As a result,the oretical precision is above 91% while the pratical one is above 85%.The result verifies that the diagrams adapt themselves to the above forest areas.The diagrams can be used in improvement cutting,forest inventory,growth forecasting and afforestation design.