[Objective] This study aimed to separate and purify antibacterial sub- stances from soil Streptomyces sp. CaiF1, and to explore the activities of this sub- stance. [Method] The antibacterial substances were separated and purified by Ethyl acetate extraction, macroporous adsorptive resin, silica gel chromatography and preparative high performance liquid chromatography （HPLC）, and powdery mildew were taken as the indicating bacterial to study their activities. [Result] Antibacterial substances were purified and the stability analysis of the extracts from Streptomyces CaiF1 fermentation broth showed very stable at pH 2.0-pH 10.0, 100 ~C and changed very little under UV treatment for 24 h. Inhibition rate of powdery mildew was 69.7%. [Conclusion] The purified antibacterial substances showed good stability, which provided theoretical foundation for their structural identifications and future ap- plications.