Abstract: The thick-skinned muskmelon ‘Jade Mushroom’ was used as the test material, and the method of root irrigation with 200,300,400 mg·L^-1 and 800 mg·L^-1 humic acid was used.When the four-leaves peroid, the day/night temperature was 10 ℃/5 ℃ for low temperature treatment.By measuring the plant height, stem diameter, fresh weight, photosynthetic fluorescence, root activity, malondialdehyde, electrolyte permeability and antioxidant enzyme activity of melon seedlings, the effects of different concentrations of humic acid on the growth and growth of melon seedlings under low temperature stress were studied, in order to provide reference for the application of humic acid in melon cold resistance.The results showed that humic acid treatment significantly increased the root vigor,chlorophyll content and net photosynthetic rate of seedlings under low temperature stress conditions,significantly decreased the cytoplasmic membrane permeability and MDA content of seedlings under low temperature stress conditions,and increased antioxidant enzymes（SOD,POD）activity,and 300 mg · L-1 treatment reached the maximum value.In conclusion,different concentrations of humic acid treatments had significant differences in photosynthetic characteristics,growth and physiological indexes of melon seedlings under low temperature stress,and the treatment with humic acid concentration of 300mg·L-1 had the best effect.