A method for assisting a memory cell in an access operation is provided. The method includes: setting a supply voltage to a first supply voltage level to determine a reference probability value of the memory cell applied by the first supply voltage level; applying an assist voltage to an access line coupled to the memory cell, and setting the supply voltage to a second supply voltage level to determine a relationship between the assist voltage and the access failure probability of the memory cell applied by the second supply voltage level; determining, from the relationship, a target assist voltage level of the assist voltage corresponding to the reference probability value; and providing an assist circuit configured to apply the target assist voltage level to the access line during the access operation, wherein the memory cell is applied by the second supply voltage level during the access operation.