The invention discloses a composite material microwave pressure molding method and device. By placing a wave-transparent pressure tank body in a microwave resonant cavity and placing a composite material in the wave-transparent pressure tank body to be heated, pressurized, cured and molded, problems that microwave energy in a circular-section pressure tank body is concentrated and hard to regulateand a pointed corner of a polygonal microwave cavity body cannot bear high pressure of gas due to stress concentration are solved; and a technical support is provided for realizing high-quality, high-efficiency and low-energy-consumption curing and molding of a high-performance composite material part.