A numerical analysis of axisymetric main nozzle flow in air jet loom has been accomplished. 4 characteristic based on upwind flux difference splitting compressible NavierStokes method has been used for obtaining basic data for an optimum design of the main nozzle for an air-jet loom and for predicting the transoni $c^ersonic flow. The static pressure on the walls of the main nozzle and flow velocity changes in the nozzle tube were calculated and analyzed by changing air tank pressures and acceleration tube lengths. The flow has reached a critical condition of Mach 1 at two position, i.e. the needle tip and the acceleration tube exit. Critical condition of flow chocking, which occurs in the main nozzle, occurs according to tank pressure at needle tip and acceleration tube exit. The tank pressure $P_T$ related to critical condition at needle tip is higher for longer acceleration tubes. On the other hand, $P_T$ related to critical condition at acceleration tube exit is nearly constant with various acceleration tube length.th.