The present invention discloses a extrusion forming method and a forming apparatus for manufacturing a self-clinching rivet, wherein the forming method comprises: upset-extruding a first end of a wire blank to shape it into a material pushing portion and a shank portion billet, upset-extruding the shank portion billet to shape it into a shank portion and a groove portion, and upset-extruding a second end of the wire blank to create a slot portion and a slot shaft portion. The invention for manufacturing the self-clinching rivet by one-time extrusion forming does not generate waste during processing, which greatly improves a utilization rate of raw materials compared with the traditional machining method. Meanwhile, a formed piece manufactured by the present invention has complete metal streamlines, which can greatly improve its strength compared with the one manufactured by machining and avoid a risk of hydrogen embrittlement in a subsequent surface treatment.