Abstract: At domestic salt rock gas storages, a large amount of insoluble substance is deposited at the bottom of storages after its solution mining is completed, due to the inherent geological characteristics of the salt rock which is used for gas storage building. The existence of deposits occupies parts of effective storage and brings a lot of adverse factors to the overall construction of the gas storage. In order to evaluate the deposits at the bottom of the cavern scientifically and accordingly take the treatment measures in the following operation rationally, it is necessary to investigate the distribution characteristics of the deposits. At first, the formation process and effects of deposits were analyzed and illustrated. Then, the insoluble deposits were sampled from laboratory experiment and its granularity distribution data were measured. Finally, its granularity distribution characteristics were analyzed based on the fractal distribution theory. It is indicated that the particle size of deposits at the cavern bottom is in linear relationship to the cumulative quantity in the double logarithm coordinate system. It means that its granularity distribution is characterized by a fractal function, and the fractal dimension, as the characteristic parameter for describing the granularity distribution, can be used to reflect the uniformity and centrality of particles. The research results provide the theoretical reference and basis for the deposit volume evaluation, the treatment measure arrangement in the following operation and the storage capacity calculation.