In order to develop a biocontrol agent with high eficiency for rice, an endophytic Streptomyces griseobrunneus Ahn75 with high antagonistic activity aganist rice blast pathogen was used as material, and the effects of different adjuvants, including nutrient, wetting dispersant, stabilizer and UV protective on the germination of Ahn75 spores and the stability of Ahn75 agent were analyzed, then the biocontrol efficencies of excellent adjuvants synergistic with biocontrol strain on rice blast was assessed. The results showed that foliar fertilizer, yeast extract, Tween 80 and dextrin could significantly promote the germination of Streptomyces Ahn75 spores, and dextrin can also protect Ahn75 spores from UV damage at a certain extent, while sodium alginate as a stabilizer showed a less effect on the germination of spores and better stability than other stabilizers. The outdoor pet experiments showed Ahn75 spore suspension combined with each adjuvant can significantly reduce the incidence and disease index of rice leaf blast. Among them, the mixed adjuvants showed best synergistic control effect with a efficacy of 38.06%. Based on the results of indoor and outdoor tests, the best formulation of Ahn75 agent was finally determined as: spore concentration 1×108 CFU/mL, yeast extract (0.05%) as nutrient, Tween 80 (0.05%) as wetting dispersant, dextrin (1.00%) as UV protective, and sodium alginate (0.15%) as stabilizer. This study provides an important basis and support for the field application of biocontrol Streptomyces Ahn75.