Provided are a non-volatile memory device, a memory system, and a method of operating the non-volatile memory device. The method includes: performing a user operation according to at least one mode selected from among a writing mode, a reading mode, and an erasing mode with respect to a memory cell array; setting up voltages of a plurality of word lines; floating at least one word line from among the plurality of word lines, the voltages of which are set up, according to the at least one selected mode; and detecting whether the at least one word line has a progressive defect, according to a result of detecting a voltage level of the at least one floated word line.