A non-volatile memory device and fabricating method thereof are provided. In the deposition to form a tunneling dielectric layer, a composite charge trapping layer and a block dielectric layer, an ingredient of a depositing material or the depositing material is adjusted to form a grading energy level structure, such that carriers are trapped or erased more easily in accordance with a variation in grading energy level. Therefore, the carriers are stored more effectively and the probability that the electric leakage occurs is reduced substantially.