Abstract: As a special extreme environment, salt lakes have enormous potential applications. To understand the characteristics of salt lake microorganism, a bacterium which isolated from a salt lake in Yuncheng was identified and its antimicrobial properties were studied. The 16s rDNA gene sequence analysis was used to identify strain AF-1; The antimicrobial activity of the fermentation broth from strain AF-1 at different temperatures, pH values and concentrations of NaCl were detected by the cylinder plate method, using Fusarium oxysporum (Strain number: 3.6855) as the indicator; Both growth/antibiotic yield curve and the antibacterial curve of AF-1 were detected; Morphological changes of treated cells on fermentation broth were observed by scanning electron microscopy and transmission electron microscopy; The functional gene screening was also studied by PCR. The results showed that AF-1 was characterized as a member of the genus of Bacillus and the antimicrobial activity of fermentation supernatant was steady at different temperatures, pH values and concentrations of NaCl; Electron spectroscopy showed that significant morphological and ultrastructure changes of cells of F. oxysporum (3.6855) were observed after treatment by fermentation broth of Bacillus sp. AF-1, and some cytoplasm is leaked from cells; The PKS genes in AF-1 genome were detected by PCR. The results meant that the Bacillus sp. AF-1 isolated from the salt lake had anti-F. oxysporum activity, such microorganisms from extremophilic environment should be developed as a potential new source of antimicrobial substances.