The invention discloses a plastic injection moulding composite board of ultrasonic welding, including a plastic panel, a plastic pallet, a injection moulding piece, the plastic panel and the plastic pallet are directly extruded to shape or shape by suction after extruding; the injection moulding piece can shape by direct injection moulding or by plural injection moulding pieces; the contact area of the injection moulding piece and the plastic panel, the plastic pallet are welded together by ultrasonic, wherein the contact area of the inner surface of the injection moulding piece and the plastic panel, the plastic pallet is provided with protruding ribs or salient points melted between the panel, the pallet and the injection moulding piece to make them connected together when the ultrasonic is welding, also an inner buried reinforcement is added between the plastic panel and the plastic pallet under the condition with higher requirement, which advance the strength and reduce the dose of plastic pieces. After adopting the structure, the plastic composite board has the advantages of low cost, few materials, easy manufacture, light quality, easy automatization, even surface, cleaness etc., which can be used in the chair board, the file cabinet, the article storing cabinet, the material frame, the wall decorative board, the wardrode clapboard etc.