The twist of polypropylene twisted yarn can make the line have certain physical functions such as strength, elasticity, elongation, luster, hand feeling, etc. The number of twists in the unit length (i.e., the number of twists per inch (T.P.I.) or the number of twists per meter (T.P.M.)) is shown in the performance of twisting the yarn to realize the twisting of yarns, which is actually to use the relative angular displacement of the cross-section of cotton yarns, so that the original straightening and parallel fibers are tilted with the axis of the yarns to change the structure of the yarns, and the twisting process of thick strips gradually shrinks from the width and gradually folds on both sides and rolls into the center of the yarn strips, forming a twisted triangle. Rough strip in the twisting process by the width of the gradual contraction, both sides gradually folded and rolled into the center of the yarn strip, forming a twisted triangle, in the twisted triangle, the width and cross-section of the cotton strip changes, from the flat strip, gradually into a cylindrical polypropylene twisted wire.