The invention discloses a preparation method of a high-strength dampproof and fireproof plate for building. The preparation method comprises the steps that (1) raw materials are prepared; (2) a phenolic resin-rosin solution is prepared; (3) slurry of a convex-concave wood grain colored surface layer is prepared; (4) a rosin solid phenolic resin material is prepared; and (5) forming is carried out on a fireproof plate production line. According to the preparation method, a fireproof plate preparation process for effectively and reasonably treating composites is achieved, operation is simple, and cost is reduced; by means of product filling alkali-resisting GRC gridding cloth and rosin phenolic resin, the strength of the fireproof plate is improved; the surface of the convex-concave wood grain colored surface layer shows a convex-concave wood grain shape, different colors can be shown, and a strong decorative effect is achieved; and according to a prepared product, the water absorption rate is smaller than 4%, the softening coefficient is about 1, the compressive strength is larger than 42 Mpa, breaking strength is high, and the fireproof and dampproof performance is good.