In this experiment, fish protein fertilizer was diluted to 1200, 1000, 800 and 500 times respectively, with clear water as the control. The watermelon plants were sprayed from the pollination stage to the fruit enlargement stage. Indicators such as the growth status of watermelon plants, fruit yield, and taste quality were measured. Variance analysis was used to comprehensively evaluate the effects of different spraying concentrations of fish protein fertilizer on the growth, quality and yield of small fruit watermelons. The results showed that watermelon treated with 500 times dilution had better performance in fruit development, plant growth and disease resistance. The average stem diameter during growth period was 7.10 mm, the average plant height was 218.15 cm, the average maximum leaf area was 699.48 cm², the average relative content of chlorophyll was 55.33, and the average nitrogen content was 18.58 mg/g. The weight of single melon was 1.22 kg, equivalent to the yield of 35428.8 kg/hm², the thickness of the peel was 0.43 cm, the content of soluble solid in the center and the edge were 10.8% and 10.0%, respectively, the taste was crisp and the fiber was less. The optimal concentration of fish protein fertilizer for small fruit watermelon is 500 times dilution.