A memory system includes a memory device including a first memory block and a second memory block; and a controller suitable for controlling the memory device, wherein the controller includes a sequential index calculator suitable for calculating a sequential index based on first logical block address (LBA) information and second LBA information that are written in the first memory block; an internal operation determining component suitable for determining whether an internal operation is to be performed on the first memory block, by comparing the sequential index of the first memory block with a threshold value; and an internal operation performing component suitable for migrating pieces of LBA information stored in the first memory block to the second memory block to rearrange the pieces of LBA information, when it is determined that the internal operation is to be performed on the first memory block.