Abstract: The Fluent of CFD is used to simulate the interior flow field of main nozzle of the air-jet looms, and a comparison has been made between the numerical simulation and experimental values arising from other investigators. The compared results show that Fluent is feasible for simulating the flow field of air-jet main nozzle. According to the values of pressure、velocity and Mach number from simulation results, weft insertion force in main nozzle can be calculted. So an approach is supplied for calculating and analyzing the weft insertion force.