Abstract: Through the indoor trial methods, the ability of inhibiting Cytospora chrysosperma by Trichoderma aureoviride was studied. After treated at 121℃ for 25 min and diluted one fold, the metabolite performed 100% inhibiting ability to mycelium growth. This inhibition ability did not change significantly within the range from pH 3 to pH 9. It indicated that inhibition ability did not relate to the changing of pH value. During the process of fermentation of T. aureoviride, single PD medium could efficiently inhibit mycelium growth of C. chrysosperma. The metabolite of T. aureoviride showed the best inhibition ability and lowest LC_50 after culturing for 3-4 days with PD medium. Shorter or longer periods of fermentation all had no benefits on inhibiting pathogen. The conductivity and respire intensity of mycelium treated by T. aureoviride metabolite were also changed. Changes of mycelium and cell wall of the pathogen were observed through optics microscope and TEM.