In order to investigate whether orchid mycorrhizal (OM) fungi can improve Dendrobium officinale seedlings ability to cope with drought stress, we investigated the effect of inoculation with OM fungi on the growth of D. officinale seedlings under drought stress using a pot experiment. The relative water content, proline content, electrolyte leakage, reactive oxygen species, antioxidant enzyme activities in leaves were analyzed. The expression patterns of antioxidant enzyme genes in leaves were analyzed using quantitative PCR. The results were as follows: (1) the biomass of D. officinale seedlings and relative water content in leaves decreased and electrolyte leakage, proline content, malondialdehyde (MDA) content, the generation rate of O-·2 and H2O2 content in leaves increased in response to drought stress compared with control. (2) D. officinale seedlings inoculated with OM fungi maintained higher relative water content, lower electrolyte leakage, MDA content, the generation rate of O-·2 and H2O2 content in leaves under drought stress. OM fungi significantly improved the growth of D. officinale seedlings under different water conditions. The plant height, mass of roots, mass of shoots and biomass of D. officinale seedlings were higher than those of control. (3) OM fungi induced the expression of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) genes under drought stress. The activities of SOD, POD and CAT were found to increase significantly in cells resulting in alleviating oxidative damage of drought stress on plasma membrane. These findings suggested that the antioxidant enzyme activities and the expression levels of antioxidant enzyme genes in leaves of D.officinale seedlings could be improved by inoculation with OM fungi resulting in enhancing the antioxidant defense of D.officinale seedlings which reduced the inhibition of drought stress on D. officinale seedling growth.