A composite board has a vacuum molded surface plate (12) and a bottom plate (13). Edges of the surface plate (12) and the bottom plate (13) are fixed into one piece by thermoplastic fixation, and a top wall of each supporting protrusion (135) and a body of the surface plate (12) are fixed into one piece by thermoplastic fixation. The composite board is formed by superimposing at least two layers of boards. A method for manufacturing the composite board provides process guidance for manufacturing the composite board.