The invention belongs to the field of oil and gas resource development, and particularly relates to a method for predicting natural gas inventory of a salt cavern gas storage reservoir. The method forpredicting the natural gas inventory of the salt cavern gas storage reservoir comprises the following steps that S1, a wellbore size and salt cavern shape parameters are obtained; S2, a gas injectionand production pipe column is divided into a plurality of injection gas pipe column micro-elements; S3, a salt cavern is divided into a plurality of salt cavern micro-elements; S4, the natural gas storage capacity of the gas injection and production pipe column and the salt cavern is calculated; S5, the natural gas inventory of the salt cavern gas storage reservoir is calculated; S6, the gas extraction amount of the salt cavern gas storage reservoir is calculated; and S7, the residual inventory of salt cavern gas storage reservoir is calculated. Compared with the prior art, the method has thefollowing beneficial effects of being suitable for salt cavern type, hard cave type and waste mining pit type gas storage reservoirs and capable of being used for predicting and calculating the maximum storage capacity, the working gas quantity, the gas extraction amount, the residual inventory and other parameters of the three types of gas storage reservoirs; and the method is clear in principleand strong in operability and can be widely popularized to on-site use after being programmed through a computer.