The invention discloses a preparation method of a mildewproof, mothproof and bacteriostatic straw plate. The preparation method comprises the following steps: smashing crop straws into particles, soaking the particles in sodium hydroxide solution and sulfuric acid solution to obtain straw fibers, mixing the straw fibers with rosemary powder, bamboo charcoal fiber, expanded vermiculite and kieselguhr separately to obtain a surface layer mixture, mixing the straw fibers with coconut carbon fiber and green bean starch to obtain a core layer mixture, paving the surface layer mixture into a die according to the odd number layer principle, paving the core layer mixture into the die according to the even number principle, and carrying out drying, thermo-compression formation, cooling, demoulding,maintaining, edge cutting and packaging to obtain a finished product. The mildewproof, mothproof and bacteriostatic straw plate is non-toxic, tasteless, formaldehyde-free, and environmental-friendly,has higher strength, is high in fireproof performance and humidity resistance, is light in weight, facilitates transportation and construction installation and can enhance memory and refresh throughrosemary. Various performance of the mildewproof, mothproof and bacteriostatic straw plate meets corresponding requirements. Furniture made of the mildewproof, mothproof and bacteriostatic straw platecan effectively prevent mildew, acarid, resist bacteria and can automatically adjust the indoor humidity.