An operating method of a memory system may include: searching for, in a memory, target map data corresponding to the read request; loading the target map data from a memory device when the target map data are not searched; compressing the loaded target map data using a predetermined compression ratio depending on an available capacity of the memory; caching the compressed target map data in the memory; parsing the compressed target map data; reading target user data corresponding to the read request from the memory device based on the parsed target map data; and outputting the read target user data.