1. A read method of a non-volatile memory device including a plurality of memory cells programmed in a first state or a second state, the method comprising: detecting the plurality of memory cells via a first read voltage for distinguishing a threshold voltage of the plurality of memory cells between the first state and the second state; outputting first data being detected from the plurality of memory cells via the first read voltage; determining whether or not to perform an over-sampling read operation based on the first data; performing the over-sampling read operation to detect the plurality of memory cells via a second read voltage, wherein the second read voltage is disposed between the first read voltage and a threshold voltage corresponding to a peak point of the first state or the second state; outputting second data detected through the over-sampling read operation; and determining read data through a soft decision algorithm based on the first and second data.