Abstract: Hemerocallis ‘Baltimore Oriole’ were used as test materials,using PEG-simulated drought stress,the effects of exogenous MeJA on the photosynthetic characteristics of Hemerocallis were studied, in order to improve the rational use of exogenous methyl jasmonate（MeJA） in the drought-resistant cultivation of Hemerocallis.The results showed that drought stress significantly reduced the day lilies photosynthetic pigment content and stomatal conductance（Gs）,transpiration rate（Tr） and intercellular CO₂ concentration（Ci）,and improved the PSⅡ initial fluorescence（Fo）,and the coefficient of photochemical quenching（NPQ）,and the largest fluorescence（Fm）,PSⅡ potential activity（Fv/Fo）,maximum photochemical efficiency（Fv/Fm） and actual photochemical efficiency（Φ PSⅡ）,coefficient of photochemical quenching（qP） were significantly suppressed,the final performance for lower photosynthetic rate（Pn）.The exogenous MeJA significantly increased the photosynthetic pigment content under drought stress.To some extent,the damage to Hemerocallis was alleviated by reducing chlorophyll decomposition and improving the stability of photosynthetic mechanism in leaves.The Gs,Ci,Pn,Fm,Fv/Fo,Fv/Fm,ΦPSⅡ,qP of leaves increased,Fo and NPQ decreased,while jasmonate metabolic inhibitor（SHAM） treatment reversed the photosynthetic characteristics of MeJA leaves under drought stress.Alleviating the damage of photosynthetic mechanism and PSⅡ reaction center of Hemerocallis leaves under drought stress,improving the electron transfer rate and light energy conversion efficiency,thus enhancing the stomatal conductance and photosynthetic ability of leaves,increasing the accumulation of photosynthetic products and improving the drought resistance of Hemerocallis.