In this study, pot experiments were carried out with Eucalyptus urophylla × E. grandis and Dallergia odorifera seedlings as research objects, and two groups of treatments and one group of control were set up as follows: E. urophylla × E. grandis was inoculated with Bacillus megaterium, but D. odorifera was not inoculated (BM); D. odorifera was inoculated with Rhizobium japonicum, but E. urophylla × E. grandis was not inoculated (RJ); neither E. urophylla × E. grandis nor D. odorifera were inoculated (control group, CK). The effects of two kinds of growth-promoting bacterial inoculation treatments on photosynthetic physiology, growth, and biomass accumulation and distribution in E. urophylla×E. grandis-D. odorifera seedlings were clarified, and the advantages of inoculation for growth promotion were also discussed. The results showed that: (1) The BM treatment significantly reduced the chlorophyll content (Chl) of E. urophylla × E. grandis (P<0.05), both BM and RJ treatments increased the plant height, ground diameter, nitrogen content of leaves, net photosynthetic rate, stomatal conductance, and transpiration rate, but decreased the intercellular CO₂ concentration. (2) The RJ treatment improved the biomass accumulation of the leaves and whole plant of E. urophylla × E.grandis and D. odorifera, while BM improved the leaves biomass of E. urophylla × E.grandis and the biomass accumulation of D. odorifera including roots, stems, leaves, and whole plant (P<0.05). (3) The net photosynthetic rates in leaves of both seedlings being positively correlated with biomass under all treatments. These results suggest that the physiological metabolism of intercropped E. urophylla × E. grandis-D. odorifera seedlings were stimulated by the inoculation of Bacillus megaterium or Rhizobium japonicum, and both growth-promoting bacteria promote the accumulation of plant biomass by boosting photosynthesis in both seedlings. In terms of biomass changes, the altruistic effect of the inoculated strains was more obvious.