Abstract: One bacterial strain against Penicillium expansum was isolated and screened from the drought soil of Gansu central habitat and named A1.The antagonistic bacterium A1 was Bacillus subtili identified by using the method of Biolog.The antibacterial activity ingredient was isolated and purified.The results of inhibiting P.expansum and Staphylococcus aureus experiment proved that one singlet compound had antibacterial activity and its minimum inhibitory concentration was 1μg /mL.The active substance had obvious inhibitory effect on a variety of microorganisms causing agricultural products and food spoilage.It had a broader antimicrobial spectrum.Especially for P.expansum and Staphylococcus aureus, its antibacterial activity was higher.It had a good application development prospects.