Abstract: The dynamic characteristics of net photosynthetic rate(Pn) and theirs difference among four varieties of Alnus crematogyne,namely,J5,J10,H1,H12,were conducted.The results were as follows:(1)The diurnal variation of Pn of these four varieties was generally classified as single-peak curve or double-peak one;and Pn of H12 and J10 was higher than that of H1 and J5 at the same time.(2)During the whole growing season,the monthly maximum value and average value of Pn of the diurnal variation of the upper crown were higher than that of the lower one.Despite of the leaf position,the two photosynthetic eigenvalue described above of H12 and J10 were obviously higher than that of H1 and J5,respectively.H12 and J10 had extremely growth significant,so they should be selected when cultivation;(3)Analysis of variance showed that Pn among different varieties,different position and different months reached highly significant difference.The Pn of J10 and H12 were remarkably higher than that of J5 and H1,and the upper crown was higher than lower crown too;and the maximum value monthly of Pn showed in June,while the minimum in Octomber;and as far as the contribution ratio of Pn was concerned,the upper crown was in the highest flight.