An operation method is used for a memory system including at least one memory device and a controller handling an operation in the at least one memory device. The method can include performing a write operation to a first region of the at least one memory device in response to a first write command set, outputting read data through reading the first region programmed in response to the first write command set, reorganizing plural write command data regarding the first write command set, based on the read data, arranging reorganized write command data based on an index of each reorganized write command data, generating estimated read data based on arranged write command data; and comparing the read data with the estimated read data to verify an operation result of the first write command set.