Disclosed is a method for producing a microcellular foam polypropylene thick board, by foaming a polypropylene motherboard by a flat foaming equipment, wherein the polypropylene motherboard bears a core structure and a pore canal structure in the core of the foam polypropylene motherboard, shortening a diffusion path of supercritical carbon dioxide into a polypropylene matrix, thus reducing the saturation time required for diffusion equilibrium and significantly increasing the production efficiency. Also provided is a method for preparing the foam polypropylene motherboard bearing the pore canal structure in the core, by extrusion molding, from general polypropylene as the raw material. The method described in the present invention may be used to produce the microcellular foam board with small cell size, high cell density and high thickness.