Roadside trees play an important role in improving transportation safety and environment conditions such as soundproof, pollutant removal, and positive psychological influence. The distribution of heavy metal concentration in the roadside tree trunks are rarely investigated in wholesome way. To know the distribution of heavy metals in tree rings has important implications for researching on heavy metals enrichment and purification effect of trees. In this study, we measured the concentration of seven heavy metals including Pb, Cd, Cr, Cu, Zn, Ni and Mn in the tree trunks of Populus tomentosa Carr. growing along Beijing Capital Airport expressway, Beijing, China, by using the Inductively Coupled Plasma(ICP). The distribution was analyzed according to the tissues, directions, and growth of the tree trunks. The influence of major climate variables on the distribution was also studied by using correlation analysis. The result showed that the average concentration of each heavy metal was different in different stem parts. The concentration ranking from high to low was Zn > Cu > Cr > Mn > Ni > Pb > Cd in xylem and Zn > Mn > Cr > Pb > Cu > Cd > Ni in bark, respectively. Heavy metal concentrations in bark were signifcantly higher than that in xylem. Moreover, the heavy metal concentrations in the tree stem near the lane side were higher than the ones farther from the lane side. The concentration of Cu, Cr, Mn, Pb, and Cd in the northfacing tree stem was higher than that in the southfacing stem. We found there were temporal variations of the heavy metal concentration level in tree stem by measuring the concentration of heavy metals in each five year tree ring segment from the tree center to the bark. The concentrations of cadmium, lead, zinc and copper had a general downward trend, but manganese, nickel and chromium an upward trend. We concluded that the tree growth and the environment influenced the distribution of heavy metals in tree rings. When tree grew slowly, the stem xylem could absorpt and deposit more the heavy metal element and vice versa. There was a significant positive correlation between Zn, Pb, Cd and Cu concentration and climate factors including annual precipitation, annual strong wind days, annual rain days and annual minimum air temperature. The estimated content of heavy metals in stem were Pb (2822.69mg), Cd (1407.55mg), Cr (21482.56mg), Cu (17255.19mg), Zn (98123.60mg), Ni (1726.46mg) and Mn (15063.84mg), respectively, on the basis of trunk biomass. The current research provided an insight for assessing the capability of Populus tomentosa to curb the heavy mental pollution under a heavy urban transportation condition.