The so-called "sawtooth thread" is a kind of thread made of special sewing materials, with inclined edges and serrated tips. During the operation, special instruments were used to minimally invasive the epidermis and introduce the thread into the subcutaneous superficial fascia tissue. Every small tooth on the sawtooth line just clings to and supports a specific part of soft tissue. The shape of the sawtooth line enables the line to firmly support the skin tissue in the soft tissue area, and enables the loose soft tissue of the face to be supported and lifted, thus shaping a new facial contour. These implanted zigzag lines will form wound tissue with scar structure, so that jagged edge is covered with many fibrous shells, thus achieving the effects of tightening skin and lifting drooping skin. Cosmetic plastic sawtooth line is made into sawtooth shape with opposite teeth on both sides of the middle part of polypropylene round line, with wide tooth root and sharp tooth end. The sawtooth line supports and bulges the flabby soft tissue of the face evenly, and can form wound tissue with scar structure. The edge of the sawtooth line is covered with many fiber shells, which has a good tightening and lifting effect on loose and drooping skin. Sawtooth thread is a new material for treating facial skin and soft tissue prolapse. It is made of high-strength polypropylene suture by fine processing, and the two ends are made into fine serrations inclined to the center.