Abstract: With supercritical CO₂ as foaming agent,polypropylene/wood flour composites were foamed by quick decreasing pressure method and the cell morphology was observed by transmission electron microscopy.By controlling the variable factors,the effects of foaming temperature,saturation pressure,decreasing pressure rate and the content of wood flour on cell morphology of foaming system were analyzed considering supercritical CO₂ dissolution,the cell nucleation and growth.Cell density and pore size were obtained by scanning electron microscopy,and their changing rule and mechanism were investigated by considering the influence of different test conditions for supercritical CO₂ foaming PP/wood powder system.