The invention provides a solid-state biofuel and a preparation method thereof. The solid-state biofuel is mainly prepared from lignin, agricultural wastes, sea mud, sepiolite fabric, aluminum oxide, a silane coupling agent, ammonium chloride, dimethyl silicone oil, yeast powder, capsaicin, di-tert-butylhydroquinone, an oxygen producer, a seismic explosion-proof agent and a bulking agent. According to the solid-state biofuel and the preparation method thereof provided by the invention, the solid-state biofuel is green and environment-friendly; by using the agricultural wastes, pollution of the agricultural wastes to air is reduced, and the recycling value is improved; compared with conventional fuel, the solid-state biofuel has the advantages of high combustion value, no emission of harmful gases after combustion, no corrosion to combustion equipment, wide sources of the raw materials, easiness in obtaining, low production cost and suitability for large-scale industrial application.