The invention discloses a preparation method for a degradable wood-plastic board. The preparation method comprises the following preparation steps: weighing bamboo charcoal microparticles, biologicalstraw powder, modified diatomite and glass fiber, adding NaOH, carrying out soaking for 12 to 24 hours, carrying out filtering to remove a solution, carrying out washing, adding deionized water, carrying out mixing under stirring, and carrying out dissolving so as to obtain a mixed base material A; weighing a degradable modified starch binder, adding a composite stabilizer, and placing an obtainedmaterial into a heating kettle at 60 to 85 DEG C, and carrying out a reaction for 2 to 4 h so as to obtain a mixed base material B; and mixing the mixed base material A with the mixed base material Bunder stirring at a stirring rate of 500 to 600 r/min at 80 to 130 DEG C, carrying out stretching, forging and extrusion, wherein the stress of extrusion is 300 to 400 N/cm<2>, introducing argon as acarrier, filling a pressurized mixture with calcium carbonate at a pressure of 1.5 to 2.0 KPa, and carrying out cooling to a room temperature so as to obtain a product. According to the invention, the modified starch binder is adopted; starch is a cheap and renewable natural polymer material and has the advantages of no toxicity, easy biodegradability and excellent environmental friendliness; thus, the starch is modified to meet the requirements of the wood-plastic board for strength, water resistance and mildew resistance in the process of application.