The invention discloses a multi-purpose fireproof high-density composite fiberboard. The multi-purpose fireproof high-density composite fiberboard is characterized by being prepared from, by weight, 42-45 parts of crop straw, an appropriate amount of sodium hydroxide with the concentration of 2%, 2-2.5 parts of a silane coupling agent kh450, 5-7 parts of vermiculite, 2-3 parts of floor gypsum powder, 66-70 parts of ethyl alcohol with the concentration of 95%, 30-32 parts of timber leftover materials, 7-8 parts of waterborne polyurethane adhesives, 1.5-2 parts of emulsified paraffin, an appropriate amount of water, 0.5-0.7 part of OP-10 and 1-2 parts of melamine phosphate. Raw materials of the multi-purpose fireproof high-density composite fiberboard can be easily obtained, the process is innovative and capable of being industrially controlled conveniently, and therefore the product can has good waterproof and fireproof performance, is high in fold-resistant tenacity, can completely replace wood plates, plastic plates and the like, can be widely used for the industries of automotive trim linings, process packages, electric appliances, furniture and the like, and is wide in application range and good in market prospect.