The invention relates to a method for manufacturing a composite board by compression molding. A mold clamping mechanism and pattern plate compression molding equipment are adopted. Standard thick pattern plates are arranged on the uppermost part and the lowest part; after materials are paved on the thick pattern plate of the lowest part through a paver, a layer of thin pattern plate is covered on the materials, the materials are paved on the thin pattern plate again; if the materials paved by the paver are uniform, a layer of thin pattern plate is covered; then, the materials are paved on the thin pattern plate until the materials paved by the paver are uniform; when the standard thick pattern plate is covered on the uppermost layer, the standard thick pattern plate on the uppermost layer is subject to mold clamping, heating and curing through the mold clamping mechanism on which a plurality of layers of materials are paved; after hot pressing is finished by a hot press, demoulding processing is performed by a demoulding mechanism; and demoulding agents can be coated on the surfaces of layers of covered thin pattern plates and other standard thick pattern plates.