Abstract: In order to conserve forest resources and make multiple uses of the forest,it is necessary to seek a minimum lumber requirement,or critical value of timber yield without affecting normal development of national economy. Based on this Critical Value,combined with the situation of forest resources,timber yield can be determined. In this paper,using the method of guantitative analysis and helped by computer,the author probed into the method to set up the critical value of timber yield and set up the critical values of timber yield with a hundred millions of value in China during each period from 1988 to 2000.