A device of submerged supersonic gas jet is configured and a two-dimensional axis-symmetric model of two-phase flow is establishedvia volume of fluid (VOF) method. The flow field of the submerged supersonic gas jet is experimentally visualized using a photographic technique which allows simultaneous analysis of the jet interface to investigate the behavior of gas jets injected into water ambient. The detailed internal structure of the flow field is obtained by numerical techniquevia finite volume method (FVM). The results show that the flow field from the nozzle exit to the far away field of downstream includes three different characteristic regions: the jet region, the transition region and the plume region. The gravity can be ignored in jet region. And the bulge and back-attack phenomena lead to the heavy oscillation flow pattern. Gas-liquid interface instabilities cause jet necking phenomena which leads expand or pinch-off of the gas jet and subsequent bulge and back-attack phenomena. A small scale of the necking results in the bulge phenomenon at upstream. A slightly larger scale of the necking causes the back-attack phenomenon. A large scale of necking even leads to the jet pinch-off phenomenon and then jet rebuilding.%针对水下超声速气体射流实验装置，分别采用高速摄影对水下超声速气体射流的形态及发展过程进行了可视化观察分析，采用VOF方法建立了二维轴对称两相数值计算流模型，对实验工况进行数值模拟，得到详细的水下超声速射流流场结构。两者结合得以研究水下气体超声速射流的形态及发展过程。研究结果表明：超声速水下射流流场明显包含射流区、过渡区和羽流区3个不同特征区域，射流区内气相的胀鼓和回击现象导致了严重的振荡流模式。气液界面不稳定性引起射流局部颈缩，从而引起颈缩上游气相截面的扩张、收缩甚至断流。可观测的小幅度的颈缩导致上游的胀鼓现象；稍大幅度的颈缩导致上游的回击现象；大幅度的颈缩甚至导致射流中断，并在随后重建射流。
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