To explore the mitigation effect and physiological mechanism of exogenous substances on the growth of Sphaeropteris lepifera under drought stress, we cultured the S. lepifera seedlings in the laboratory were subjected to natural drought stress, and sprayed the leaves with 1.0 mmol/L SA solution, 150 μmol/L MT solution, 100 mg/L PP₃₃₃ solution, 2.5 mmol/L CaCl₂ solution and 0.3 mg/L EBR solution to determine the growth, photosynthesis, antioxidant enzymes, osmotic mediators and other related physiological indexes of seedlings. The results showed that: (1) compared with normal growth control (CK), drought stress significantly inhibited the growth of aboveground part and significantly promoted the growth of underground part of DCK; drought stress also significantly inhibited the activities of antioxidant enzymes in leaves, aggravated the damage to the cell membrane, and caused a significant increase in the electrolyte and MDA content in the leaves of the S. lepifera seedlings, and also significantly increased the accumulation of osmotic regulators; drought stress also significantly reduced the chlorophyll content in the leaves, which could not carry out normal photosynthesis, and its net photosynthetic rate, stomatal conductance and transpiration rate were significantly reduced. (2) Compared with DCK, foliar spraying of exogenous substances can significantly improve the antioxidant enzyme activities of seedling leaves, effectively remove excessive reactive oxygen species in cells, significantly reduce the relative conductivity and malondialdehyde content, make the metabolism of cell membrane system normal, reduce the damage caused by drought stress to S. lepifera seedlings, and improve the net photosynthetic rate, stomatal conductance, transpiration rate and chlorophyll content, effectively reduce the inhibition of drought stress on photosynthesis. (3) The comprehensive evaluation of membership function method showed that the treatment of appropriate concentration of salicylic acid (SA) and melatonin (MT) had the best mitigation effect on drought stress of S. lepifera seedlings.