The instability of the cavity-making string of the salt cavern gas storage will not only reduce the efficiency of the cavity-making operation, but also affect the quality of the cavity, and even cause the difficulty in pulling out the string and the failure of the cavity. The vibration control equation and fluid motion equation of cavity making string are established by matching the process flow of salt cavern gas storage. The numerical solution of cavity making string is realized using ANSYS Fluent commercial software. According to the field M well parameters of Jianghan oil field and the similarity principle, a vibration simulation test bench for cavity making string is designed. The experimental data are compared with the calculation results of the numerical simulation model, and the correctness of the numerical simulation model is verified. The effects of injection flow rate on the vibration instability of the cavity making string are investigated. It is found that the larger the injection flow rate is, the greater the initial displacement of the cavity making string is, and the larger the deformation of the string is, which will cause instability. It is very important to reduce the flow velocity in the cavity-making pipe as far as possible while meeting the cavity-making construction schedule, so as to prevent the static buckling or chaotic motion instability of the cavity-making pipe string. The conclusions obtained provide a theoretical basis for the selection of cavity-making construction parameters.