A memory device includes a memory cell array, a current detector and a controller. The memory cell array has a plurality of memory cell strings coupled to a common source line. The current detector detects a circulating current on the common source line or a power end of a page buffer. The controller is configured to: during a program operation, perform a first program operation on a plurality of first memory cells corresponding to logic 0 according to a first program verify voltage, and perform a second program operation on a plurality of second memory cells corresponding to logic 1 according to a second program verify voltage, where the first program verify voltage is different from the second program verify voltage; and provide a read voltage to the memory cell strings during a read operation, and sense the circulating current based on a read current reference value.