Abstract: In order to provide directionally genetically improved breeding materials of poplar by exploring the phenological traits genetic variation level and its development potential of Populus deltoides and carry out the resource evaluation, the author observed and analyzed 8 phenological phases in seedling period of 60 Populus deltoids clones introduced from America. The results showed that: (1) there was obvious difference in phonological character among clones, especially in lamina stage and late deciduous stage, with the largest variation coefficient of 14.97% and the minimum of 3.83% respectively. (2) The time of lamina stage was most scattered while that of late deciduous stage was most concentrated. The phonological character in the early stage of seedling growth was the main factor influencing the length of growing season. (3) By principal component analysis, the author classified phenological phases into 3 typical periods, including germination stage, lamina stage and deciduous stage. (4) The author classified 60 clones into 4 types by using clustering analysis in phenological time variables of clones.