Abstract: 【Objective】 To explore the effects of the application of bitter bean seed alkaloids with special fertilizers for melons and fruits and urea on the yield and quality of watermelon and clarify its effects on the yield and quality of watermelon. 【Methods】 A field trial was conducted with watermelon varieties: Black Pearl (A₁), New Superior No. 2 (A₂) and Anon No. 2 (A₃) as the test materials, and four treatments were set up in the trial, with three replications for each treatment: treatment 1 (T₁): aqueous solution of bitter bean seed alkaloids; treatment 2 (T₂): special fertilizer for melons and fruits; treatment 3 (T₃): urea; and treatment 4 (CK): a control conventional basal fertilizer treatment, respectively. The effects of bitter bean alkaloid application on the yield and quality of three watermelon varieties were analyzed. 【Results】 The treatment with aqueous solution of bitter bean seed alkaloids significantly increased the economic and biological yields of the three watermelon varieties; significantly increased the soluble solids, vitamin C content and fruit hardness, and reduced the nitrate content and fruit hollowness. The three varieties showed better yield increase and improvement in single fruit weight, yield, soluble solids content, hardness, fruit hollowness, nitrate content and vitamin C content. Single fruit weight increased by 59.95%, 73.03% and 55.52%, respectively, compared with control CK. Yield increased by 59.45%, 74.98% and 57.91% over control CK, respectively. Soluble solids content increased by 49.46%, 47.38% and 44.95% over control CK, respectively. Hardness increased by 28.16%, 25.98% and 47.38% over control, respectively. Fruit hollowness was reduced by 92.38%, 83.96% and 86.3%, respectively, over the control. Nitrate content was reduced by 25%, 30.94% and 34.64%, respectively, over the control. Vitamin C content increased by 69.84%, 73.08% and 65.67%, respectively, over the control. 【Conclusion】 Bitter bean seed alkaloids can significantly increase the soluble solids content, vitamin C content, hardness and ripeness of watermelon, while reducing nitrate content and fruit hollowness. And the application with conventional compound fertilizer has a significant effect on the yield and fruit quality among its various watermelon varieties, and performs better in a number of testing indexes.