The invention relates to plastic profile machining dies, in particular to a macromolecule foaming co-extrusion skirting line die. The macromolecule foaming co-extrusion skirting line die comprises a connecting body, a transition plate, a support plate, a converging plate and a mouth die plate, all of which are sequentially in butt joint. The macromolecule foaming co-extrusion skirting line die is characterized in that a co-extrusion plate is additionally arranged between the converging plate and the mouth die plate, and the outer end of the mouth die plate is in butt joint with a water jacket plate; a skirting line cavity is formed in the co-extrusion plate, and a pre-forming cavity communicating with the skirting line cavity is formed above the skirting line cavity; a pressurizing cavity communicating with the pre-forming cavity is formed above the pre-forming cavity; the co-extrusion plate is further provided with an arc supply way and a feeding way communicating with an arc material way, and the two ends of the arc material way communicate with the left end and the right end of the pre-forming cavity correspondingly; and a skirting line cavity is formed in the water jacket plate, and cooling water ways are arranged above and below the skirting line cavity. The macromolecule foaming co-extrusion skirting line die is simple in production and operation and high in yield, produced skirting line products are good in quality and attractive in appearance, and the macromolecule foaming co-extrusion skirting line die is mainly used for producing and machining macromolecule skirting line profiles.