The invention discloses a preparation method of a biodegradable nanometer material. The preparation method comprises the following steps: crushing soybean meals and fibrous residues, adding 1.0 to 2.0mol/L of a sulfuric acid solution into a mixture and impregnating for 1 to 3 hours; subsequently carrying out centrifugal stirring and filtering and washing with distilled water to neutral; then adding isoamyl acetate, polypropylene and polyethylene glycol, and carrying out stirring reaction at the temperature of 60 to 80 DEG C for 1 to 2 hours; carrying out ultrasonic treatment for 15 to 20 minutes to obtain a mixed solution A; adding the mixed solution A into a single screw extruder and extruding under the conditions that the extrusion temperature is 85 to 110 DEG C and the rotating speed of a screw is 80 to 90 r/min; putting the mixed solution A into a mould of a hot press; carrying out hot pressing under the conditions that the temperature is 130 to 150 DEG C and the pressure is 15 to20MPa for 3 to 10 minutes, so as to obtain the biodegradable nanometer material.