Abstract: The air velocity in reed groove could be tested to analysis the influence of process parameters for the weft insertion. In this article, the pitot tube is applied to test the air velocity at different positions in reed groove by the instrument designed, and the adjusting range of jet angle and relay nozzle distance is studied. The results indicate there are different velocities at different positions; when the supply pressure is 2～4×105Pa, the jet angle of relay nozzle could not be 5º, or the air velocity for weft insertion will be too low; shortening the relay nozzle distance is helpful to improve the average air velocity in reed groove, and when the relay nozzle distance is 65mm the air velocity in reed groove could satisfy the weft insertion requirement of 100 m•s-1 completely.