The invention provides a plant fiber base floor brick which sequentially comprises a tile, a plant fiber inorganic composite material and a Portland cement plate. Crop straws or plant fibers processed by agriculture and forestry processing residues or crushed aggregates and inorganic adhesive are compounded to prepare the plant fiber inorganic composite material, the abrasion-resistant, waterproof and high-hardness tile and the fireproof, formaldehyde-free and low-hardness plant fiber inorganic composite material are perfectly compounded and integrated through epoxy resin glue, release of artificial formaldehyde is omitted, fireproof grade reaches B1 or more, a substrate of each layer of the floor brick is an inorganic substance, heat expansion and cold contraction rate is small in difference, and the floor brick is not easily deformed. The invention further correspondingly provides a preparation method of the plant fiber base floor brick. Waste crop resources and the agriculture and forestry processing residues are effectively utilized, materials are low in cost and wide in source, rigorous parameter requirements avoids easy layering among the tile, a plant fiber inorganic composite layer and the Portland cement plate, and durability is high.