The invention discloses an automatic seam abutting device for cutting pieces and a seam abutting method of the automatic seam abutting device. The automatic seam abutting device comprises a machine table, a control device, an air sucking device, a stamper device, a positioning device, a feeding device and a sewing device, wherein the air sucking device is provided with a plurality of air sucking holes, and the air sucking holes are formed in a table surface of the machine table; the stamper device is provided with at least one pressing arm and a stamper driving device for driving the pressing arm to move; the positioning device is provided with at least one positioning arm and a positioning driving device for driving the positioning arm to move; the air sucking device, the stamper device, the positioning device, the feeding device and the sewing device are connected to the machine table, and the air sucking device, the stamper driving device, the positioning driving device, the feeding device and the sewing device are electrically connected to the control device. The automatic seam abutting device for the cutting pieces involved by the invention is suitable for the seam abutting technology of most collars, the requirements for the skills of workers are greatly lowered, and the production efficiency is improved.