A method of decoding data of a non-volatile memory device is provided. The method includes a first decoding operation of reading first hard decision data from the non-volatile memory device using a first hard decision read level and performing decoding using the first hard decision data; a second decoding operation of reading first soft decision data from the non-volatile memory device when the decoding fails in the first decoding operation, and performing decoding using the first soft decision; and a third decoding operation of changing from the first hard decision read level to a second hard decision read level when the decoding fails in the second decoding operation, reading second hard decision data using the second hard decision read level, and performing decoding either using the second hard decision data or using both the second hard decision data and the first soft decision data.