a u2032 respectively wherein the s twist short staple yarns b and b u2032 are at the inner side of the cotton rovings a and a u2032 the drafted two rovings a and a u2032 and two s twist yarns b and b u2032 are output from the front jaw 10 and enter the twisting triangle area to be twisted and then are wound onto a yarn bobbin 7 via a guide wire 6 to produce the z twist untwisted yarn with parallel fiber in center and winding fiber on the surface in order to improve the count of the yarn one s twist short staple yarn can be fed and this yarn is between two rovings a and a u2032 in this process the z twist untwisted yarn with parallel fiber in center and winding fiber on the surface can also be produced two rovings a and a u2032 from the roving bobbin enter the draft mechanism to be drafted through two guide funnels 1 and 1 u2032 in parallel respectively wherein the roving a is made of viscose staple fiber and a u2032 is made of polyester staple fiber two polyurethane filaments b and b u2032 are fed from the back of the front roller 5 via a guide wire or a guide wheel the polyurethane filaments b and b.