Abstract: The fiber length(l) and width of 7 poplar clones were measured and studied in this paper.It shows there are no significant differences in variation of fiber length at breast height in 6,8,and 11 years old among 7 poplar clones.The order of fiber length is lI69>lI72>lNL895>lNL1388>lNL447>lNL351>lNL95 among 7 poplar clones of 11 years old.The fiber length of I69 is 6.6% longer than NL95 within 11 years old.Fiber length and fiber width gradually increase from pith to bark,but fiber width variation is not so remarkably like fiber length.Within a single tree fiber length is the shortest at the base of trees and increases from base to peak,and it reaches the longest at above 5.6 m within the tree.After maintaining stabilization to 17.6 m it starts to declines within a single tree.The mean fiber width is the widest within 3.6 m,but it will decrease above 3.6 m in a single tree.The notable linear,polynomial,index and power relationship exist between fiber length and growth rings.And linear,polynomial,index regression mainly exist between fiber length and tree height.But the physiological age would affect fiber shape trait in poplars.