A controller, an operating method thereof, and a memory system including the same are disclosed. The controller includes a controller for controlling a nonvolatile memory device according to a request from a host with a host memory. The controller includes an address unit configured to divide regions of the host memory, which is allocated as a host memory buffer (HMB), to generate a plurality of sub HMB regions, determine index values of the plurality of sub HMB regions, and generate an HMB map table by mapping virtual addresses to the index values; and a memory control module configured to access at least one among the plurality of sub HMB regions based on the HMB map table. The virtual addresses may be set to continuous values with respect to the plurality of sub HMB regions.