Abstract: Based on the data collected from 344 sample plots, the design mainly deals with the stand density control diagram for Pinus yunnanensis, which is made in accordance with the theory and methods used at home and abroad, and combiaing practical growing conditions of the above-mentioned species in the Nanpanjiang Forest Region. In the parts of drawing up the stand density control diagram, it gives a brief account of the methods about collecting and arranging the data, and illustrates the meaning of the density control curves, the mathematical models and the drawing methods. Then the equations of the density control curves of the diagram for Pinus yunnanensis in the forest region are deduced on the basis of regressive calculation of the collected data. By using the equation and the conventional drawing methods, the values in couples are drawn up in the lg N-lg V coordinate system spotted in the double-logarithmic coordinate paper. By doing so, the points of the values are smoothly coanected into groups of curves, and the stand density control diagram for Pinus yunnanensis has been formed. In the parts of application precision test both in theory and practice, the equivalent height curves of trees and the curves of equivalent D. B. H. have been tested by means of the unused data collected frotn fieldwork. The test results come out respectively as 82.2% a^d 93.5% in theoretical precision, and 85.5% and 87.1% in practical precision. The test proves that the design is basically qualified for practical use in production. Examples of the methods and range of the diagram/ application are also introduced.