The invention belongs to the technical field of microbes, and discloses a Toona sinensis endophytic fungus 56-50. spore Alternaria mali ; Preservation unit: General Microbiology Center of China Microbiological Culture Collection Management Committee, preservation address: Institute of Microbiology, Chinese Academy of Sciences, No. 3, No. 1, Beichen West Road, Chaoyang District, Beijing, preservation date: September 30, 2016, preservation number: CGMCC No. 12980. The present invention isolates an endophytic fungus from the stem of Toona sinensis for the first time Alternaria mali , the secondary metabolites of the bacteria have good inhibitory effect on Pseudomonas aeruginosa and Proteus. The preparation of Toona sinensis endophyte 56-50 ( Alternaria mali ) The method for secondary metabolites is simple and easy, and the cost is low.