A memory device, includes a memory array for storing a plurality of vector data each of which has an MSB vector and a LSB vector. The memory array includes a plurality of memory units each of which has a first bit and a second bit. The first bit is used to store the MSB vector of each vector data, the second bit is used to store the LSB vector of each vector data. A bit line corresponding to each vector data executes one time of bit-line-setup, and reads the MSB vector and the LSB vector of each vector data according to the bit line. The threshold voltage distribution of each memory unit is divided into N states, where N is a positive integer and N is less than 2 to the power of 2, and the effective bit number stored by each memory unit is less than 2.