The invention belongs to the technical field of building materials and particularly relates to a plant fiber outer wall board with stone textures and a preparation method of the plant fiber outer wall board. The plant fiber outer wall board comprises an upper surface material layer, a medium material layer and a lower surface material layer, wherein the upper surface material layer and the lower surface material layer are prepared from the following raw materials: early-strength sulphoaluminate cement, water, a plant fiber and an admixture; the medium material layer is prepared from the following raw materials: early-strength sulphoaluminate cement, water, plant fiber and admixture; alkali-resistant chopped fiberglass meshes are paved into the upper surface material layer, the medium material layer and the lower surface material layer; and the stone textures are arranged at the outer side of the upper surface material layer. In addition, the invention further provides a method for preparing the outer wall board. The plant fiber outer wall board with the stone textures is low in density and high in toughness and has the stone textures at the product fabrication stage, and the additional cost for later decoration is reduced. The adopted raw materials are cheap and available, and the production cost of the product is reduced.