With chilling sensitive watermelon ‘linglongwang’ as the tested material,we investigated the effects of exogenous 50 mg/L NAA,25 mg/L 6-BA,25 mg/L GA³,25 mg/L ABA on chilling injury index,the main content of active oxygen and the activity of antioxidant enzymes of watermelon seedlings under low temperature stress.The results showed that:(1)The appropriate concentration of 6-BA,GA³ and ABA could significantly reduce the chilling injury index of watermelon seedling,while NAA worked in the opposite direction.(2)At the third day of cold stress,the generation rate of O^-·2 and the content of MDA in watermelon seedling that GA³,ABA and 6-BA pretreated were significantly reduced by 9.0%,9.4%,7.7% and 38.1%,40.1%,45.9%,respectively;and the content of H²O² of watermelon seedling were reduced by 11.9%,18.9% and 22.7% at the fifth day of cold stress.(3)6-BA,GA³ and ABA pretreatment made SOD activity significantly increased by 15.95%,17.87% and 18.33% at the seventh day of cold stress,respectively;POD activity significantly increased by 36.36%,73.74% and 145.45%,respectively;CAT activity significantly increased by 115.22%,116.28% and 161.63%,respectively.Hence,it was indicated that appropriate concentration of exogenous 6-BA,GA³ and ABA could effectively improve the activities of SOD,POD and CAT,slow down the acumination of H²O² and O^-·2 as well as MDA,mitigate the damage of low temperature in watermelon seedling under low temperature stress,then strengthen the cold resistance of watermelon seedling.Furthermore,25 mg/L 6-BA showed the best effect,could be applied to production.