With melon variety ‘Hamilü’ as the tested material,we investigated the effects of 10~200 μmol·L^-1 exogenous salicylic acid (SA) on melon seedlings growth,chlorophyll content,gas exchange parameters and chlorophyll fluorescence under cadmium(100 mg·L^-1 Cd²⁺) stress by substrates culture.The results showed that:there were significant effects on the growth and photosynthesis function under cadmium stress.However,the best effect on the alleviation of Cd²⁺ stress damage was observed in the treatment of 100 μmol·L^-1 SA.At this concentration,the seedlings growth,chlorophyll content,net photosynthetic rate (Pⁿ),stomatal conductance (G^s),transpiration rate(T^r),photosystem Ⅱ(F^v/F^m),excitation capture efficiency of open centers(F^v′/F^m′),actual photochemical efficiency (Ф^PSⅡ),photochemical quenching coefficient(q^P) and the fraction of photochemical efficiency (P) in leaves were significantly increased,while minimal fluorescence(F⁰),non-photochemical quenching coefficient (NPQ) and excess energy (E) were significantly decreased.The above results indicated that dosage effect of SA existed on the alleviation of Cd²⁺ stress in melon seedlings,and the best alleviating effect on Cd²⁺ stress damage was 100 μmol·L^-1 SA,which was favorable for the seedlings to maintain photosynthesis,improve photochemical electron transport efficiency,capture and converse solar energy thus improving melon growth.