The invention relates to the technical field of biological organic bacterial fertilizers, and discloses a composite biological organic bacterial fertilizer and a preparation method thereof. The composite biological organic bacterial fertilizer comprises the following raw materials in parts by weight: 88-176 parts of crop straws, 12-22 parts of rape seed cakes, 5-14 parts of a straw fermenting agent, 200-360 parts of water, 18-26 parts of a chemical fertilizer, 7-16 parts of a mixed microbial agent, 2-7 parts of acrylic acid, 3-5 parts of potassium persulfate, 6-14 parts of polyacrylamide, 5-9 parts of tetramethrin and 2-8 parts of permethrin. The composite biological organic bacterial fertilizer of the invention realizes the mechanism of improving the nitrogen supply capability of soil by applying the straw bio-organic fertilizer and the inorganic nitrogen fertilizer, promotes the absorption of plants to nutrients, has the effects of inhibiting and killing soil pathogenic microorganisms, improving the disease resistance of crops and improving the continuous cropping harm, provides a healthy growth environment for plants, has good pest resistance, protects the growth environment of the plants, and improves the survival rate of the plants.