Abstract: For efficiently designing high performance interlacer jet which was used for filaments interlacing, this paper simulated compressible airflow inside yarn duct with commercial CFD software ANSYS CFX and then compared the results with the former experimental results. It can be seen that the simulated results has good agreement with the experimental ones except for few points. Furthermore, the distributions of airflow velocity on cross-section of yarn duct show that symmetric eddy help to produce tangling parts; the distributions of airflow velocity on lengthwise-section show that tangling parts are difficult to be produced in higher yarn tension and the radial direction velocity in the vicinity of yarn duct center decides the opening of filaments.