Abstract: Gas injection and brine discharge is an indispensable stage for the construction and operation of salt-cavern gas storage, and the measurement and control of gas-brine interface is the key technology of gas injection and brine discharge. The existing measurement methods cannot do the measurement continuously and their cost is high. To solve these problems, an optical fiber interface measurement technique was developed in this paper. The distributed optical fiber measurement technique is adopted in this technology. The temperature is measured with the downhole optical fiber, and the location of the gas-brine interface is judged according to the inflection point of the temperature curve. This method is advantageous with simple operation, wide detection range, low monitoring cost and continuous measurement. In the practical engineering application, this optical fiber interface measurement technique is proved reliable when compared and evaluated with the existing measurement methods. It can be used not only in the gas injection and brine discharge of salt-cavern gas storage, but also in the process of solution mining under nitrogen and gas, so it has wide application prospect.