The invention discloses a memory array and its operating method. The memory array contains multiple memory cells which are arranged in multiple columns and rows, wherein multiple parallel memory strings are corresponding to the respective rows; multiple word lines are arranged to be vertical to the memory strings; and each word line is connected to multiple gate electrodes of a corresponding column of the columns of the memory cells. According to the method, programming operation is executed; the programming operation programs all memory cells on the multiple edge word lines, which are positioned on an opposite side of the memory array; the programming operation operates multiple selective memory cells in the memory array according to input data to be stored in the memory array; and the selective memory cells are positioned among the edge word lines. Threshold voltage of each programmed memory cell is positioned at programming verifying level.