This paper employs the methods of computational fluid dynamics to simulate the internal flow field of Air-Jet nozzles to analyze the interlacing characteristics of yarn processed in cylindrical nozzles. The three-dimensional turbulent compressible flow field inside Air-Jet nozzles is calculated by solving the continuity, momentum and energy equations incorporated with a turbulence model. Additionally the yarn characteristics in two cylindrical nozzles are measured experimentally. It is found that the interlacing density of yarn has a linear dependence on the axial vorticity of air flow inside the nozzle.