Abstract: Aimed at providing basis for a high yield and good quality production of watermelon, the effect of biological organic fertilizer on watermelon growth, yield and quality under protected cultivation conditions was studied in a field plot experiment with three treatments:biological organic fertilizer application (BOF), organic fertilizer application (OF) and conventional fertilization (CK). The results showed that BOF improved watermelon growth significantly. Compared with those of OF and CK, the main tendril in BOF increased 15.2% and 10.9%, the SPAD value in BOF increased 9.9% and 6.7%, and the watermelon bearing position in BOF was increased 10.3 cm and 14.5 cm, respectively; however, BOF had no significant effect on leaf numbers and stem diameter. Compared with OF and CK, BOF also significantly increased the fruit numbers and yield:the fruit number increased 7.6% and 11.6%, and the yield increased 14.5% and 17.9%, respectively. The yield of BOF reached 46 860 kg/hm². BOF could improve the soluble solids content (SSC) or decrease the rind thickness of the watermelon to some extent, although there was no significant difference (p>0.05) between treatments.