Abstract: As we all known, a wellplanned fertilization method plays a very important role in poplar seedling production. This paper focused on the question whether formulated fertilization is good for the the growth of poplar seedling and it explores the best one in final. In the relative experiment for this question, nine kinds of formulated fertilizer solutions mixed with N，P，K at different concentration ratio were used during the growing process of poplars named as Populus deltoids Bartr.cv.‘Lux’× P.deltoides Bartr.cv.‘Havard’. The results showed that the nine kinds are all favorable for poplar seedling growth and the third one with N，P，K at concentration ratio of respectively 17 mg/L, 10 mg/L and 8.5 mg/L, mostly increased the biomass for the root, bark, branch, leaf and all of them as a whole.Comparing with the control, they are increased by 294%, 66%, 96%, 126% and 118% respectively. According to the regression equation for the data obtained from the experiment above, the rational concentration of N，P，K for seedling’s growth of poplar was 1303 mg/L,3.76 mg/L and 2.24 mg/L respectively, while for the root growth that was 2.36 mg/L, 2.12 mg/L and 471 mg/L respectively. Therefore, the amount of fertilizer N should be increased in the early stage of growth when the fertilizer P and fertilizer K were being used, but in later stage of growth the amount of fertilizer N should be controlled properly and in turn the amount of fertilizer P and fertilizer K should be increased, which was favorable for improving stress resistance and equality of the poplar’s seedlings. So the formulated fertilization would promote the growth of seedling and root of poplar and increase the biomass production, in particular, N was good for growth of seedling height and tissue biomass, while as K was favorable for root growth.