Microbial biocontrol agents SL19 has strong antimicrobial activity to many plant pathogens. By morphological, physiological and biochemical experiments and 16S rDNA sequence homology analysis, SL19 was identified as Bacillus velezensis. Antifungal spectrum was confirmed by confrontation tests. The results showed that SL19 has significant inhibitory effect against Verticillium dahilae, Fusarium oxysporum, Botrytis cinerea, Rhizoctonia solani, Sreptomyces scabies, etc. Active substances were separated and purified using ammonium sulfate method, and physical and chemical properties were studied. Antifungal substances were heated at 60 °C, 80 °C for 20 min, respectively, and antifungal activity has no difference; After 100 °C treatment for 20 min, antifungal activity decreased to 75.3% of the control; after 120 °C treatment for 20 min, antifungal activity was completely lost. Antifungal substances were not sensitive to trypsin, pepsin, proteinase K, UV radiation and chloroform. SDS-PAGE analysis revealed that the antifungal substances contained a kind of about 50 kD protein. It can be preliminarily concluded that the antifungal substance secreted by this strain was mainly protein. Tests suggested that the antifungal protein could inhibit the growth of hyphae and spore germination of Verticillium dahilae. The study on this strain would provide theoretical basis for biological control.