The invention discloses a composite bio-formulation for preventing crop diseases, comprising the following raw materials: trichoderma pseudokoningii fermenting liquid, bacillus subtilis fermenting liquid, water-soluble chitosan, sodium glutamate residue liquid and potassium humate, wherein the trichoderma pseudokoningii and the bacillus subtilis are high-effect strains which are obtained after being screened and processed, later the fermenting liquid of the trichoderma pseudokoningii and the bacillus subtilis is obtained through a submerged fermentation technique, and the composite bio-formulation for preventing crop diseases is obtained through combining. The composite bio-formulation for preventing crop diseases in the invention has obvious effects for preventing blight, verticillium, gray mold, phytoph-thora capsici leonian, downy mildew, powdery mildew, gray mold, fulvia fulva and so on, and can be especially used for preventing the blight and the verticillium which have large danger in agriculture. The invention is suitable for preventing the diseases and improving yields of various vegetables, melons, fruits and crops, such as tomatoes, chili peppers, eggplants, cucumbers, watermelons, apples, Chinese chives, cottons and so on.