A method for producing a microcellular foam polypropylene thick board by foaming a polypropylene motherboard with a flat foaming equipment, wherein the polypropylene motherboard bears a core structure having one or more rows of pore canals in the centre, characterised in that: the flat foaming equipment comprises a special supercritical flat foaming equipment comprising: a hydraulic system for supplying clamping pressure; a temperature control system for supplying heat; a pressure gas delivery system for supplying supercritical fluid; a flat foaming mold; a flash blow-down system; and a gas recovery system, and that the method comprises the following steps: the flat foaming mold is heated up to the foaming temperature by the temperature control system for supplying heat; the polypropylene motherboard bearing the core structure having one or more rows of pore canals in the centre is placed into the flat foaming mold, which is driven by the hydraulic system for closing; upon pressurizing up to 15-20 MPa by the hydraulic system, the high pressure and high temperature gas is introduced into the flat foaming mold by the pressure gas delivery system until the gas pressure is up to 5-25 MPa; the high pressure and high temperature gas is diffused from the surface and core structure of the polypropylene motherboard into the polymeric matrix, with the saturation time required for diffusion being 30-200 minutes; and upon dissolution in equilibrium, the gas within the flat foaming mold is blown down by the flash blow-down system and is recovered by the gas recovery system; when the mold is opened, the polypropylene motherboard pops out of the mold and foams to give the microcellular foam polypropylene material. the flat foaming equipment comprises a special supercritical flat foaming equipment comprising: a hydraulic system for supplying clamping pressure; a temperature control system for supplying heat; a pressure gas delivery system for supplying supercritical fluid; a flat foaming mold; a flash blow-down system; and a gas recovery system, and that the method comprises the following steps: the flat foaming mold is heated up to the foaming temperature by the temperature control system for supplying heat; the polypropylene motherboard bearing the core structure having one or more rows of pore canals in the centre is placed into the flat foaming mold, which is driven by the hydraulic system for closing; upon pressurizing up to 15-20 MPa by the hydraulic system, the high pressure and high temperature gas is introduced into the flat foaming mold by the pressure gas delivery system until the gas pressure is up to 5-25 MPa; the high pressure and high temperature gas is diffused from the surface and core structure of the polypropylene motherboard into the polymeric matrix, with the saturation time required for diffusion being 30-200 minutes; and upon dissolution in equilibrium, the gas within the flat foaming mold is blown down by the flash blow-down system and is recovered by the gas recovery system; when the mold is opened, the polypropylene motherboard pops out of the mold and foams to give the microcellular foam polypropylene material. the flat foaming mold is heated up to the foaming temperature by the temperature control system for supplying heat; the polypropylene motherboard bearing the core structure having one or more rows of pore canals in the centre is placed into the flat foaming mold, which is driven by the hydraulic system for closing; upon pressurizing up to 15-20 MPa by the hydraulic system, the high pressure and high temperature gas is introduced into the flat foaming mold by the pressure gas delivery system until the gas pressure is up to 5-25 MPa; the high pressure and high temperature gas is diffused from the surface and core structure of the polypropylene motherboard into the polymeric matrix, with the saturation time required for diffusion being 30-200 minutes; and upon dissolution in equilibrium, the gas within the flat foaming mold is blown down by the flash blow-down system and is recovered by the gas recovery system; when the mold is opened, the polypropylene motherboard pops out of the mold and foams to give the microcellular foam polypropylene material.