A memory system may include: a nonvolatile memory; a volatile memory; and a controller suitable for repeatedly entering and exiting from an automatic exclusive mode for each predetermined size of write data transferred from the host in a start period of the automatic exclusive mode, and allocating the volatile memory exclusively for performing a merge operation on the nonvolatile memory during an entry period of the automatic exclusive mode, the controller may include a command queue for storing plural commands transferred from the host, may use a predetermined operation in the start period of the automatic exclusive mode to calculate a processing time of write commands among the commands stored in the command queue and an entry time of the entry period of the automatic exclusive mode, and may schedule a processing order of the commands stored in the command queue according to the calculation result.