Abstract：Primary studies on relationship between high temperature and humidity and soil water with watermelon〔Citrullus lanatus（Thunb.）Matsum.et Nakai〕flesh degeneration were conducted by covering plastic tunnel and different irrigation treatments．The results showed that under high temperature，both soil drought and high soil humidity could cause the increase of watermelon flesh degeneration index，and the flesh degeneration index under soil drought condition was the highest．The flesh degeneration index of the plants irrigated at the noon was 4-12 times of that irrigated in the morning．These results indicated that soil water was an important environmental cause for watermelon flesh degeneration．Soil drought or high soil humidity and irrigating at noon were causes for watermelon flesh degeneration．Besides，exposure under sun could also lead to watermelon flesh degeneration.
