This study developed a novel biological suspension seed coating agent by formulating the Bacillus velezensis strain XY40-1-based biopesticide suspension with film-forming agents, warning dyes, and synergists. Using eggplant as the test crop, the quality and efficacy of the formulation were systematically evaluated. The results showed that by integrating with film-forming agents(6% polyvinylpyrrolidone), warning pigments(0.4% alkaline fuchsin), and synergists(50 nmol/L pyrroloquinoline quinone), the quality of the prepared seed coating agent meet the national standards, with live bacterial count of 2.5×109 cfu/mL, pH of 7.647, with qualified film-forming properties and pourability, and with 92% coating uniformity, a detachment rate of 7.67%, and a viscosity of 100 mPa?s. In the greenhouse cultivation trial, eggplant seeds were treated with a seed coating formulation at a agent to seed ratio of 1∶35, and the results showed that the germination potential, germination rate, and emergence rate of eggplants in the experimental group increased by 364.77%, 13.49% and 67.43%, respectively, compared to the control. Moreover, the seed coating agent demonstrated enhanced efficacy against Phomopsis blight, with disease incidence being reduced by 40.42% and disease index being reduced by 38.26%.