Abstract: This paper, using range analysis and variance analysis methods of orthogonal experiment study, tries to look for important factor and general factor that influence the wraping effect of the parallel ply yarn from the air pressure of Z-nozzle, network nozzle, S-nozzle, to judge if the air pressure of each nozzle has obvious effect on yarn quality. Then try to find the best pressuer combination. The conclusion is: the air pressure of network is the most important factor affecting the wrapping effect, and it has the most obvious effect on yarn quality; pressures of S-nozzle and Z-nozzle are general factors, and they don’t have obvious effect on yarn quality. Meanwhile the best air pressure combination is 0.1MPa (S-nozzle)，0.2 MPa(network nozzle)，0.1MPa(Z-nozzle). At this time, the hairiness-index of parallel ply yarn is the least, that means the hairiness has wrapped around parallel ply yarn well and the location of single yarns is fixed best in the ply yarn.