The invention discloses trichoderma harzianum Sch234 bactericide as well as a preparation method and an application thereof. The preparation method of the trichoderma harzianum Sch234 bactericide comprises the following steps of: (1) firstly activating a trichoderma harzianum bacterial strain Sch234 on a PDA flat plate, then inoculating the trichoderma harzianum bacterial strain Sch234 on a PDA inclined plane to be cultured, adding deionized water for sterilization, preparing spore suspension, adding tween-20 until final concentration of the tween-20 in the spore suspension is 0.025%, and adjusting the concentration of the spore suspension to be 1.5*10<6>/ml; (2) mixing dry substrate oatmeal with rice husk uniformly, adding water, and carrying out high-pressure steam sterilizing; and (3) inoculating the prepared spore suspension with substrate in ratio of 10ml per bag, cultivating, and drying in the air and grinding, thus the trichoderma harzianum Sch234 bactericide is obtained. The trichoderma harzianum bacterial strain Sch234 has a strong parasitic effect on rice sheath blight disease and hypha and sclerotium of sclerotinia sclerotiorum, control effect of antibiological inoculant to rice sheath blight disease under field cultivation condition is 83%, an application method in soil treatment is simple, labour force is saved, and the trichoderma harzianum bacterial strain Sch234 can be used for producing biopesticide and is safe to people and livestock.