Abstract: Using matured Thompson seedless grape under extreme drought conditions and deep pit infiltration irrigation technique, the effect of different irrigation quotas on grape sugar content and fruit shape index was determined. The results show that grape fruit shape index and sugar content follow a normal distribution curve. Fruit shape index and grape sugar content were divided into six groups by fuzzy cluster analysis method. After averaging, a good fuzzy relation was observed between grape fruit shape index and sugar content. A fuzzy model for the fruit shape index and sugar content with irrigation quota as parameter was established. From the model, the relationship between fruit shape index and sugar content as influenced by irrigation quota is distinct. This study further proves the impact of irrigation quota on fruit shape index and sugar content.