Abstract: Poplar is one of the major fast-growing tree species in China, but little was known about the effect of auxin on fast growth and secondary growth of poplar plants. In this study, PtrFBL1 for auxin receptor gene was cloned in poplar, the over-expression vector of PMDC32-PtrFBL1 based on PMDC32 was constructed and 17PtrFBL1 over-expressed plants of P. alba × P. glandulosa cl. '84K' were obtained. The root, growth and photosynthetic indexes of 3 transgenic lines and the control were analyzed. The results showed that the total root length and total root area of transgenic lines were higher than those of the non-transgenic control lines, and the differences were all significant or extremely significant. On the other hand, the mean adventitious root length, mean adventitious root diameter and root biomass were not significant. The plant height, average internode length, average internode diameter and ratio of height and diameter were higher than these of the control lines. In addition to lower limitation of stoma(Ls), all the other indexes, i.e. the stomatal conductance(Cd), water use efficiency(WUE), light use efficiency(LUE) and relative contents of chlorophyll were higher than those of the controls, and the differences from most transgenic lines reached significant or extremely significant levels. The transgenic lines increased the root areas, and had stronger photosynthetic efficiency and rate of water consumption, and promoted biomass accumulation on ground, thus had the accelerated speed of growth. Therefore, the PtrFBL1 gene has the potential to be manipulated to improve the growth.