In order to find out a new way for environment-friendly and resourcelized utilization of cassava starch processing wastewater, the cassava starch anaerobic fermentation liquid was applied in watermelon production, and its effects on the growth and development, yield and fruit quality of watermelon were investigated. The results showed that the cassava starch anaerobic fermentation liquid significant- ly promoted the vegetative and reproductive growth and improved the yield and fruit quality of watermelon. Compared with conventional fertilization, the application of cassava starch anaerobic fermentation both with COD concentration of 1 200 mg/L according to the amount of 150 t/hm2 promoted the growth of vines and leaves of watermelon plants, brought forward the flowering, fruiting and harvest of watermelon and significantly increased the fruit number, fruit weight, yield, fruit size, fruit shape index, soluble solid content, soluble sugar content, soluble protein content and Vita- min C content of watermelon. At the same time of improving the yield and quality of watermelon, cassava starch anaerobic fermentation liquid was turned into treasure as a liquid fertilizer. This study provides a new ideal for the yield and quality im- provement of watermelon and the wastewater treating of starch factories.