A special core material for exterior wall external insulation fire-proof insulation and decoration plates and a preparation method thereof are provided. The core material comprises a blocky vertical silk rock wool plate blank. The six sides of the vertical silk rock wool plate blank are each coated with a layer of flexible building structure adhesive to form a sealing layer. The outer side of the sealing layer is reinforced with basalt fiber mesh cloth, and the basalt fiber mesh cloth closely wraps the vertical silk rock wool plate blank to form a new mesh-bar composite body. Therefore, the joint stress of the pasting material and the vertical silk rock wool plate blank is enhanced, the tensile resistance, compressive resistance and shearing resistance of the rock wool insulation plate are increased, and the strength, stiffness, crack resistance and integrity of the rock wool insulation plate are improved. The surface of the vertical silk rock wool plate is sealed, so that the plate is effectively prevented from aging or becoming damp, and the service life is prolonged greatly. The core material has a simple structure, and is easy to manufacture. The technical scheme is applicable to the special core material for exterior wall external insulation fire-proof insulation and decoration plates.