Abstract: Based on the basic technology principle of salt cavity shape control during cavity dissolution, and supposed that the gas and brine in the cavity are not dissolved, mathematic models of interface depth is established by using nitrogen as a gaseous state protector material, and computation models of gas injection volume is given when the interface between gas and brine is stable in salt cavity. Taking the salt cavern solution mining in Jintan Basin as an example, nitrogen injection volume and interface depth between nitrogen and brine are calculated while taking nitrogen as a gaseous state protector material, meanwhile, economic cost of protectors between nitrogen and diesel are analyzed and compared. The result indicates that using nitrogen as a protector can reduce construction cost of salt cavern gas storage.