The invention relates to a method for preparing rigid polyurethane foam by utilizing microwave liquefaction products of bamboo processing residues, which is characterized in that: polyethylene glycol 400, glycerol and ethylene carbonate mixed liquefaction agent, 98% sulfuric acid and dried and pulverized bamboo The processing residue is put into a three-neck bottle, and placed in a microwave liquefaction reactor with functions of condensation, stirring, and infrared temperature measurement for microwave heating. After the reaction is completed, neutralization reagents are added to neutralize the liquefied product to pH 7-8 , to obtain plant polyols. Then, mix and stir the plant polyol prepared above with polyether polyol, catalyst, curing agent, water, silicone oil, and foaming agent evenly, then add MDI, nano-activated carbon or titanium dioxide, mix and stir for 10s-15s, and put it into the mold. Stand at room temperature for foaming, curing, and demoulding to obtain rigid polyurethane foam. The invention makes full use of bamboo resources, reduces the cost of liquefaction, the liquefaction product can be used in all components, and realizes the goal of converting all components of bamboo processing residues into synthetic polyurethane raw materials. The product has the characteristic of being able to absorb PM2.5, and is a An environmentally friendly bio-based polyurethane rigid foam product.