The machine adopts a single straight needle, a shuttle hook, and upper and lower compound feeding to form a double-thread lock stitch, and is equipped with a back-sewing device, which is easy to operate. Due to the use of a special upper and lower feeding mechanism and a presser foot cross lifting mechanism, when sewing bulky sewing materials and medium-thick materials with high potential for migration, the upper and lower layers can be fed in the same amount; overlapping sewing and climbing at high and low levels In slope sewing, the feed is cool, the stitch length is stable, and the stitches are smooth and beautiful. The machine can be adjusted according to the special requirements of the sewing process, so that the difference between the feeding amount of the upper sewing material and the feeding amount of the lower sewing material meets the expected requirements, and the sewing quality and the sewing effect are obviously improved.