A memory system includes: a memory device including a plurality of memory blocks; and a controller for dynamically changing a size of a write buffer based on whether a current workload is a sequential workload or a mixed workload, wherein the controller includes: a workload detecting unit suitable for changing current workload from the sequential workload to the mixed workload based on a read count, or from the mixed workload to the sequential workload based on a write count; and a write buffer managing unit suitable for reducing the size of the write buffer when the current workload is changed to the mixed workload.