Abstract: Salt cavern gas storage is constructed by solution mining, and it is necessary to conduct regular sonar survey and string adjustment according to the effective volume of the salt cavity. For this purpose, a calculation method for the effective cavity volume of salt cavern gas storage was proposed, including the determination method of brine discharge concentration and the mathematical model for calculation of the effective volume. The argentometry was used to determine the brine discharge concentration, with which the volume of salt mined could be calculated. Then, the formulas for calculating the effective cavity volume, the total volume of salt bed used and the volume of the expanded insoluble could be derived by following the conservation principle of salt cavity volume. Finally, check calculation was performed for the formulas with Cavity A of Jintan Gas Storage as the example. According to the results, the brine discharge concentration is about 300 g/L, close to saturation, the average mining speed is 230 m³/d, and the cavern forming rate is 79%, which approaches the average level of Jintan Gas Storage group. Conclusively, this method with high calculation accuracy can satisfy the requirements of field application and can be used to effectively guide the site operations.