Abstract: Muskmelons ( Cucumis melo L.cv.Yu jin xiang) fruit were used as material, and were dipped in hot water at 53℃, chitosan at 2% and chitosan at 2% combined with hot water at 53℃ for 10min, respectively, to study the effect of three treatments on the lesion diameter of fruit inoculated with T.roseum, the key enzyme activities and substances accumulation of phenylpropanoid pathway. The results indicated that all treatments decreased lesion diameter, hot water and the combination of hot water and chitosan treatments showed better control, were 47.41% and 41.78% lower than the control after 7d of treatment. The hot water and the combination of hot water and chitosan treatments also increased the activity of phenylalanine ammonia - lyase ( PAL) and 4 - coumarate CoA ligase ( 4CL) in fruits, the activity of PAL was 3.32 and 2.8 times higher after 9d of treatment, and 4CL was 32.5% and 25.3% higher than the control after 12d of treatment, respectively.The combination of hot water and chitosan treatment significantly enhanced the content of total phenolic, flavonoid and lignin. The content of total phenolic, flavonoid and lignin was 32.8% , 50.76% and 71.61% higher than that in the control after 15d of treatment. It is suggested that hot water and the combination of hot water and chitosan treatments increase the resistance against T.roseum in muskmelon fruit by inducing phenylpropanoid pathway.