In order to estimate poplar biomass by using forest inventory of poplar planting trees, while applying software SPSS12.0, according to collected materials of 23 sample trees of I-72 Poplar biomass in wuzhi county, the allometric equation has been designed to estimate poplar biomass. Biomass Expansion Factor (BEF) function and the ratio of the weight of the root to the weight of the shoot (RSR) function of stand description factors were established by forest inventory and allometric equation and then the total stand biomass was computed according to the growing stock and basic wood density. The results of function curve estimation show that BEF and RSR have very good relevance to stand average height, basal area, stand age and stand volume, and the value of BEF is about 1.3 and the value of RSR range from 0.14 to 0.6,and reduces with the value of forest inventory increases. The study could offer a quality basis for using forest inventory of poplar planting trees to estimate poplar biomass.