Extrusion molding is one of the earliest and most widely used technologies in the polymer processing field. But there are some problems in the traditional extrusion, such as die swell, distortion and deformation. The further development and application of the polymer extrusion molding are seriously restrained. Polymer gas-assisted extrusion is a new molding process developed at the beginning of this century. A stable gas layer is formed between the die inner wall and the melt surface and the polymer melts are extruded in a fully slip and non-adhesive manner for the lubrication of gas layer. The melt flow field distribution is improved in the polymer gas-assisted extrusion molding and the inherent problems are effectively reduced or even eliminated affecting the traditional extrusion product quality. The gas-assisted extrusion technology has been widely concerned after being invented by many scholars because of its excellent characteristics such as energy saving, environmental protection and improving product quality. And the research results about it have important scientific significance for enriching and developing polymer molding theory. It will also promote the further development and application of the technology. The research advances of gas-assisted extrusion molding technology were summarized in China and other countries in this paper. The gas-assisted extrusion molding mechanism and equipment were introduced. The research methods and results were reviewed about gas-assisted extrusion, gas-assisted co-extrusion, gas-assisted micro-tube extrusion and gas layer. And the research trends of gas-assisted extrusion were prospected.