Abstract: The paper presents an experimental study on dynamicinstability of submerged supersonic gas jets. The gas-jet flow patterns arerecorded at real time by a high-speed camera. The development process ofsupersonic and subsonic gas jets and the process of the unstable flowpattern are visualized clearly. The patterns of the unstable jet flow areanalyzed in detail. The frequencies of bulging and back-attack of the jetare calculated from the experiment data. The experimental results indicatethat the frequency of the back-attack increases with increasing the bulgingfrequency, and the frequency of the bulging increases with increasing thestagnation pressure ratio P_0/P_b. Comparison of the data from the twokind of unstable patterns indicates a certain relevance between bulging andback-attack: Both the bulging and back-attack are all initiated by pressureoscillation inside of the gas jets and have a strong randomness, and thebulging is a kind of representation of energy storage before back-attackhappens. In addition, when the energy storage gets to a certain limit, aback-attack event will be occurring.