Abstract: During the experiment of gas/liquid coaxial swirl injector conducted with air and water under atmospheric environment,it is observed that the injector may self-oscillate.The self-oscillation periodically occurs and vanishes with the increasing velocity of the gas flow.Then,a theoretical model is presented based on the experiment investigation.Simulation of the acoustic process has been performed and conclusions consistent with the experiment can be drawn from the theoretical model,which explains the experimental phenomena quite well.At last,the comparison between phenomena of the self-oscillation and some experiments of LRE indicates that some instability phenomena in Oxygen/Hydrogen propellant rocket engine may be the result of self-oscillation in coaxial swirl injectors.