The effects of jet impingement and turbulence structure on jet mixing rate arc investigated by using a simultaneous measurement system of concentration and velocity. It is found that, after the end of injection, dispersion of momentum of a CO2 jet Is much faster than that of concentration. The residual gas is then left in a rather quiescent atmosphere, that makes a sluggish mixing process of the residual gas. Jet impingement can create intensive air motion in the near impingement region, that promotes the mixing of the residual gas. However, the effect of jet impingement decreases as the distance from the impingement point increases.