The chlorophyll fluorescence parameters of potted oil peony ‘Fengdan’ seedlings inoculated with arbuscular mycorrhizal fungus Gigasporarosea under severe drought(soil relative water content is 30%) and mild drought(soil relative water content is 55%) stress for 3 and 6 days were compared and analyzed. The results showed that the potential PSII activity Fv/Fo and performance index PIabs of ‘Fengdan’ seedlings inoculated with arbuscular mycorrhiza were increased under different drought stress compared with the non-inoculated seedlings. Compared with the non-inoculated treatment, in inoculated ‘Fengdan’ with 3 and 6 days under severe drought stress, Mo significantly decreased by 14.5% and 29.8% respectively; Vj significantly decreased by 12.9% and 16.2% respectively; φEo significantly increased by 9.7% and 52.2% respectively; and φo significantly increased by 8% and 23.6%, respectively. Compared with the non-inoculated treatment, in inoculated ‘Fengdan’ with mild drought stress for 3days and 6 days, absorption of energy per unit area(ABS/CSo), capture of light energy per unit area(Tro/CSo), quantum yield electron transfered per unit area(ETo/CSo), quantum yield transfered at the end of PSⅠ per unit area(REo/CSo) were improved, but with no significant difference. Compared with the non-inoculated treatment, in inoculated ‘Fengdan’ with under severe drought stress for 3 and 6 days, Tro/CSo were significantly increased by 37.8% and 41.1% respectively, ETo/CSo significantly increased by 47.7% and 73.8% respectively, and the number of response centers per unit area(RC/CSm) significantly increased by 50.1% and 141.8%, respectively. Under drought stress, regulatory energy dissipation quantum yield Y(NPQ) of inoculated ‘Fengdan’ was significantly higher than that of non-inoculated ‘Fengdan’, and non-regulatory energy dissipative quantum yield Y(NO) was significantly lower than that of non-inoculated. The research showed that arbuscular mycorrhizal can improve PSII reaction center activity under the drought stress, especially under the severe drought, increase the absorption and capture of light energy, improve the efficiency of electron transfer ability and light chemistry, at the same time, more remaining energy distributed in the form of heat dissipation, avoid the light damage, then improve drought resistance and photochemical activity of oil tree peony seedlings under drought stress.