Decay caused by fungal pathogens is responsible for significant economic loss of muskmelon fruit (Cucumis melo L.) in China. However, postharvest treatment is not effective in controlling all of these pathogens, owing to the ability of some of them for latent infection. Therefore, preharvest treatment has been considered as a promising method to control postharvest decay in muskmelon fruit. The effect of multiple preharvest treatments with harpin on postharvest disease and quality of cv. ‘Huanghemi’ muskmelon fruit was investigated in this study. Results showed that harpin treatment significantly decreased the incidence of latent infection caused by Alternaria alternata and Fusarium spp. in harvested fruit. Meanwhile, the postharvest pink rot in treated fruit inoculated with Trichothecium roseum was suppressed noticeably. Moreover, preharvest treatment increased the activities of peroxidase, phenylalanine ammonia lyase, 4-Coumarate:CoA ligase and β-1,3-glucanase compared with control fruit. Harpin treatment also contributed to the accumulation of total phenolic compounds and lignin. In addition, harpin treatments were able to maintain the quality of harvested fruit. These results suggest that multiple treatments with harpin before harvest may be a promising technology to control postharvest disease and delay quality losses in Huanghemi muskmelon fruits.