Abstract: To investigate the effect of air flow in an air?-vortex spinning nozzle on yarn forming through twisting fiber strands,a computational fluid dynamics(CFD) model has been developed to simulate the air flow characteristics in an air-vortex spinning nozzle.Two-dimensional simulation and standard k-ε turbulence model is used.The computational results show that the velocities in the nozzle are transonic.Velocity and static pressure distributions in the nozzle are presented and analyzed.Due to the centrifugal and twisting forces generated by tangential velocity,the rear ends of the fibers are separated from the fiber strand and spread out.Then they helically wound round the fiber strand to form a real-twisted yarn.In the upstream of the jet orifices,the pressures are lower than the atmosphere pressure,which is helpful for sucking the fiber strand coming out from the front roller nip into the nozzle.This work shows that CFD technique can provide a better understanding of the behavior of the high speed air flow in the air-vortex spinning nozzle.