Abstract: On the basis of studying the correlation between the degree of superiority of the dominant contract method and the differential value of the sample plot method, nine regression equations used to estimate the differential values of height, DBH and volume of Pinus taeda and Pinus elliottii by the degree of superiority of the corresponding trait, and two regression equations for estimating the differential value of volume by only the degree of superiority of DBH(for P. taeda) or that of height(for P. elliottii) were established. A three-dimension conversion table was established, in which selection rate(P) and selection intensity(i) can be found out directly according to the differential value(U). The basis of determining the prescribed minimum of the superiority degree was posed. The method of estimating the genetic gain and selection effect was simplified. Besides, it was found when the value of i increases and closes to the value of U, the value of P decreases rapidly, therefore, in superior tree selection, it is not a good idea to determine the value of i at a very high level, otherwise, few superior tree can be selected.