[Background] The gray mold disease caused by Cladosporium tenuissimum is a common fungal disease infecting protected bottle gourd, often resulting in serious economic losses. [Objective] To identify strain hjt6 with antagonistic activity against the gray mold disease of bottle gourd and evaluate the growth characteristics and antifungal activity of the strain, so as to provide microbial resources for the biocontrol of the gray mold disease of bottle gourd. [Methods] Strain hjt6 was identified based on morphological, physiological, and biochemical characteristics and 16S rRNA gene and gyrB gene sequences. The growth curve of the strain was established, and the temperature, pH, and salt tolerance was examined. The broad-spectrum antagonistic effect of this strain was evaluated by the mycelial inhibition assay. Plate confrontation, co-culture, and detached fruit re-inoculation were conducted to assess the disease control efficacy of strain hjt6 against C. tenuissimum. [Results] Strain hjt6 was identified as Bacillus velezensis. It grew within a temperature range of 10 ℃ to 50 ℃, with an optimal growth temperature of 30 ℃. It could grow within the range of pH 5.0–9.0, with pH 7.0 being the most suitable. The strain tolerated 0% to 10% NaCl. Strain hjt6 exhibited inhibitory activities against eight crop pathogens, with the inhibition rates ranging from 57.38% to 82.18%. It showed an inhibitory ability of “++++” and an inhibition rate of 71.53% against C. tenuissimum on plates. The co-culture results showed that the strain hjt6 reduced the mycelial mass of C. tenuissimum by 77.31%, and achieved the control efficacy of 92.63% on the detached fruits inoculated with the pathogen. [Conclusion] Strain hjt6 demonstrates promising antagonistic effects against the gray mold disease of bottle gourd and could serve as a valuable microbial resource for the biocontrol of this disease.