Abstract: The strength of the vortex twist acting on the air jet vortex yarn was investigated by analytical model based on simulating the flow field inside the nozzle.The result shows that the strength of the vortex twist acting on the air jet vortex yarn is regarded as a function of the number of jet orifices,jet orifice angle,diameter of the jet orifice,inner diameter of the nozzle,outer diameter of the hollow spindle,velocity at the entrance of the jet orifice(namely nozzle pressure),distance between the entrance of the hollow spindle and the entrance of the nozzle,the projecting height of open-trail-end fibers twined over the top exterior of the hollow spindle and yarn diameter.Increasing the velocity at exit of the jet orifice increases the strength twisted by the whirled airflow.The strength twisted by the whirled airflow increases with decreasing the inlet diameter of the nozzle block and becomes weaker with increasing the distance from the inlet of the nozzle block to the inlet of the hollow spindle.The strength twisted by the whirled airflow enhances with increasing the outer diameter of the hollow spindle.The numerical results show the effectiveness of analytical model.