A non-volatile memory device includes a memory cell array including a plurality of multi-level cells each storing data corresponding to one of a plurality of states of a first group of states, and a control circuit. The control circuit is configured to program data corresponding to one of the plurality of states in a first multi-level cell according to a first verify voltage level of a first group of verify voltage levels, and to control the first multi-level cell to be re-programmed to one of a plurality of states of a second group of states according to a first verify voltage level of a second group of verify voltage levels. Each voltage level of the second group of verify voltage levels has a higher level than the verify voltage levels of the first group of verify voltage levels.