Abstract: A three-dimensional computational fluid dynamics model was developed to simulate the flow field inside the nozzle of air jet vortex spinning with 3-D CFD & Fluent 6.2.Flowing state,distributing of static pressure and velocity inside the nozzle of air jet vortex spinning were characterized and analyzed.Relationship between flowing state and structure of the yarn was also discussed.The research shows that compressive air through the jet orifice comes into being three-dimensional whirly airflow inside the nozzle,the tangential airflow and the arial airflow are fit for the theory of swirling airflow,the tangential velocity twists open-trail end edge fibers;the draw effect of the axial velocity to fibers may be neglected;the radial velocity makes the edge open-trail end fibers in the main nozzle begin to expand to let yarn get more wrapper fibers,static pressure distributions take on the U shape along nozzle radius,the reason of twist irregularity of air jet vortex yarn is the degree twisted at different position is different for separated edge open-trail end fibers.