The earthworm hydrolysate was rich in amino acids that had a significant positive effect on crop growth. In order to study the effects of earthworm amino acid topdressing on watermelon yield and quality，the earthworm amino acid topdressing with different dilution ratios(800，500 and 300 dilution ratios)sprayed on the leaves of watermelon at the fruit expansion stage was conducted in this study，and water and urea topdressing were used as control. The results showed that the watermelon yield in urea topdressing was equivalent to that in water topdressing. Compared with water and urea topdressing，watermelon yield increased by 19% and 18% in earthworm amino acid 800 dilution ratio. The sugar content and organic acid content of watermelon in urea topdressing were higher than those in water topdressing，while，the sugar-acid ratio in urea topdressing was lower than that in water topdressing. Compared with water topdressing，earthworm amino acid at 300，500 and 800 dilution ratios showed the higher sugar content in watermelon and earthworm amino acids at 800，500 dilution ratios showed the lower content of organic acids and the higher sugar-acid ratio. Compared with urea topdressing，earthworm amino acid at 300，500 and 800 dilution ratios maintained the same sugar content in earthworm amino acid topdressing，while reduced the organic acid content，therefore increased the sugar-acid ratio，especially，the organic acid content was the lowest and the sugar-acid ratio was the highest in earthworm amino acid at 800 dilution ratio. The nitrate content of watermelon in urea topdressing was equivalent to that of water topdressing. Earthworm amino acid at 300，500，800 dilution ratios showed significantly lower nitrate content in watermelon than that in water and urea topdressing，especially at 800 and 500 dilution ratios. The soluble protein content of watermelon in urea topdressing was lower than that in water topdressing. Compared with water and urea topdressing，earthworm amino acid at 800 and 500 dilution ratios could significantly increase the content of soluble protein. The Vitamin C(Vc) content of watermelon in urea topdressing was similar with that in water topdressing. Compared with water and urea topdressing，earthworm amino acid at 500 and 300 dilution ratios could increase the Vc content. Overall，spraying appropriate concentration of earthworm amino acid on the leaves of watermelon during fruit expansion stage was beneficial to improve the yield and quality of watermelon，and earthworm amino acid at 800 dilution ratio showed the best effect.