The invention discloses a straw board for a floor and a manufacturing method and application of the straw board. The manufacturing method comprises the following steps that rice straws are cleaned upwith water, dried and crushed to obtain a straw crushed material; the straw crushed material is taken to be stir and wash in water, extruding, dehydrating and drying are conducted on the washed straws, the straw crushed material is added into sodium hydroxide solution, ultrasonic soaking at room temperature is conducted, the straw crushed material is neutral after water washing, soaking at room temperature with sulfuric acid solution is conducted after drying, and the straw crushed material is neutral after water washing; the straw crushed material is soaked into sodium silicate solution to obtain straw fibers after drying finally, a hydrophobic material and a modifier are added into the straw fibers, the obtained straw fibers are sent into a stirring-type glue sprayer, a spray gun is arranged in the stirring-type glue sprayer for glue spraying, and the straw fibers are uniformly mixed with an adhesive by stirring; and the straw fibers mixed with the adhesive are transferred into a mould press, and pre pressing and hot pressing in the mould press after paving are conducted to obtain the straw board. By means of the method, the mechanical properties of the board are improved while the application amount of the adhesive is reduced, meanwhile, the product has hydrophobicity and fireproof performance, and secondary processing molding is facilitated.