Using E. angustifolia and G.biloba G.Don var.parviflora 2-year-old seedlings, the effects of drought stress on gas exchange and protective enzyme activities were conducted. Four treatments were arranged: control (CK), light drought (T1), moderate drought (T2) and heavy drought (T3). Results showed drought stress not only caused the decline of net photosynthesis rate, transpiration rate, stomatal conductance and intercellular CO2 concentation of two species, but also changed the diurnal pattern to a certain extent. Under light and moderate stress, the decline of net photosynthetic rate of two species was caused by stomatal factors, however, under heavy stress, this mainly by non-stomatal factors.Instantaneous water use efficiency of E. angustifolia showed the tendency of increase -decrease-increase, but G.biloba G.Don var.parviflora always decreased. Apparent light use efficiency of two species decreased by 50%. Apparent light use efficiency of G.biloba G.Don var.parviflora was more sensitive to drought stress. The changing tendency of apparent CO2 use efficiency of two species decreased. The diurnal pattern of apparent CO2 use efficiency of E. angustifolia shifted from a single-peaked curve(T1) to a double-peaked curve(T2),then a single-peaked curve (T3), while it always showed single-peaked curve in G.biloba G.Don var.parviflora. With the drought stress increasing, the activity of superoxide dismutase(SOD), peroxidase(POD), catalase(CAT)of two species first increased and then decreased. When the content of soil moisture was above 128%, the activity of SOD of the two species was higher than that in CK. With soil water content decreasing, the activity of SOD of the two species was lower than CK. Under heavy stress, although the activity of POD in E. angustifolia decreased, it was still higher than CK, but no significant difference was observed between T3 and CK in G.biloba G.Don var.parviflora.The activity of CAT of two species was significantly lower than CK under heavy stress. With the drought stress increasing, the content of malondialdehyde(MDA) of two species in the leaves increased. and the lipid peroxidation of G.biloba G.Don var.parviflora was more impacted by drought stress.