An operating method of a memory system includes preprogramming multi-page data of a memory controller to a nonvolatile memory device, generating a state group code based on multi-bit data of the multi-page data, and each state group data of the state group code having less number of bits than corresponding multi-bit data, detecting sudden power-off occurring after the preprogramming, backing up, in response to the detecting of the sudden power-off occurring, the state group code to the nonvolatile memory device, recovering, after power is recovered from the sudden power-off, the multi-page data from the nonvolatile memory device, based on the state group code, reprogramming the multi-page data to the nonvolatile memory device, and reprogramming, in response to the detecting of the sudden power-off not occurring, the multi-page data of the memory controller to the nonvolatile memory device.