Abstract: 【Objective】This study aims to clarify the bacteriostatic activity of the fermentation powder of Bacillus subtilis Yz strain on cotton seedling diseases, and screens the formula for seed pelleting agent with the decline rate of live spores and the germination rate of cotton seeds as indicators.【Method】The antibacterial activity of Yz strain fermentation powder against cotton damping-off, cotton anthracnose, and cotton red rot was determined by the confrontation culture method. In addition, by orthogonal design L9(33), the effects of different additives on the decline rate of live spores of fermentation powder of B. subtilis Yz strain and the germination rate of cotton seeds were determined to screen the best formula for seed pelleting agent.【Result】The corrected inhibitory zone diameter of fermentation powder of B. subtilis Yz strain with 50 times dilution for cotton damping-off, cotton anthracnose, and cotton red rot were 10.07mm, 15.54mm and 8.96mm, respectively. And the diameter of inhibitory zone decreased gradually with the decrease of the concentration of fermentation powder. The best additives were diatomite, sodium carboxymethyl cellulose and sodium lignosulfonate. 【Conclusion】The fermentation powder of B. subtilis Yz strain show good antibacterial activity against cotton dampingoff, cotton anthracnose, and cotton red rot. The optimum proportion is 3(diatomite) ∶ 0.8(sodium carboxymethyl cellulose) ∶ 0.1(sodium lignosulfonate) ∶ 1(Yz fermentation powder).