This paper analyzes the essence of the method of purposive sample plot, which has long been applied in Soviet Union and in China. It also discusses the method of determining the age of technical maturity and that of quantitative maturity of forest on the basis of the information of forest management survey (subcompartment survey) and continuous forest inventory (C. F. I.) with the aid of the tested standard tables. It suggests a new and economical way for determining the maturity and felling age of forest to forestry enterprises as well as the provinces where C. F. I. system has been established.