NOVELTY - Preparing biomass fuel involves collecting plant straw and then drying, cutting and crushing the collected material into 90 meshes to obtain straw powder for further use. The straw powder is dried to reduce water content to 25% and then the dried material is mixed with modifying agent in mass of 50:1.5 at 80-85 degrees C. The mixed material is stirred at 20-30 minutes and then the stirred material is cooled to room temperature. The cooled material is kept in freezing device at 15 degrees C for 40 minutes to obtain modified straw powder for future use.    USE - Method for preparing biomass fuel (claimed).    ADVANTAGE - The method enables to prepare biomass fuel with good fuel performance, less smoke and high thermal efficiency.    DETAILED DESCRIPTION - Preparing biomass fuel involves collecting plant straw and then drying, cutting and crushing the collected material into 90 meshes to obtain straw powder for further use. The straw powder is dried to reduce water content to 25% and then the dried material is mixed with modifying agent in mass of 50:1.5 at 80-85 degrees C. The mixed material is stirred at 20-30 minutes and then the stirred material is cooled to room temperature. The cooled material is kept in freezing device at 15 degrees C for 40 minutes to obtain modified straw powder for future use. The 85 pts. wt. modified straw powder is added with 3 pts. wt. calcined kaolin powder, 2 pts. wt. sea mud, 2 pts. wt. sepiolite, 5 pts. wt. carbon fiber, 1 pts. wt. aluminum oxide, 2 pts. wt. tobacco cellulose, 2 pts. wt. modified corn starch, 1.5 pts. wt. antioxidant, 0.5 pts. wt. linear polyethylene, 0.4 pts. wt. silane coupling agent, 0.2 pts. wt. ammonium chloride, 0.5 pts. wt. dimethyl silicone oil, 0.3 pts. wt. styrene monomer, 0.3 pts. wt. polyethylene glycol and 2 pts. wt. stabilizer in molding apparatus to perform extrusion molding. The modifying agent comprises 10-15 pts. wt. graphene microchip, 5-10 pts. wt. rare earth oxide, 15-20 pts. wt. xylitol solution, 2-4 pts. wt. yeast powder, 1-3 pts. wt. capsaicin, 2-4 pts. wt. nano silicon nitride and 2-3 pts. wt. hydroxypropyl-beta-cyclodextrin. The antioxidant comprises 20 pts. wt. dimethyl ketoxime, 25 pts. wt. peanut oil, 4 pts. wt. soybean separated protein, 2 pts. wt. azelaic acid, 3 pts. wt. purple sweet potato anthocyanin, 0.5 pts. wt. ethanediol, 4 pts. wt. isoamyl acetic acid, 2 pts. wt. graphite, 2 pts. wt. hydroxypropyl-beta-cyclodextrin, 10 pts. wt. silicone oil, 4 pts. wt. palm oil, 3 pts. wt. liquid paraffin and 4 pts. wt. teert.-butanol. The antioxidant is prepared by utilizing all components.