The invention discloses a culture medium for producing trichodermin by trichoderma harziarum strain L through fermentation, and belongs to the technical field of microorganisms. The method comprises the following steps of: adding inactivated Fusarium oxysporiumf.sp.cucumeris mycelium powder into a culture medium for the trichoderma harziarum strain L for fermentation culture; centrifuging fermentation liquor; and analyzing the content of the trichodermin in the fermentation liquor by adopting a gas chromatogram, wherein the concentration of the trichodermin in the fermentation liquor after the inactivated Fusarium oxysporiumf.sp.cucumeris mycelium powder is added is improved by several times than that of a contrast. The invention provides a feasible method for improving the fermentation level of producing the trichodermin of the trichoderma harziarum strain L.