A method for performing a physical unclonable function generated by a non-volatile memory write delay difference includes a resetting step, a writing step, a detecting step, a terminating step and a write-back operating step. The resetting step includes resetting two non-volatile memory cells controlled by a bit line and a bit line bar, respectively. The writing step includes performing a write operation on each of the two non-volatile memory cells. The detecting step includes detecting a voltage drop of each of the bit line and the bit line bar, and comparing the voltage drop and a predetermined voltage difference value to generate a comparison flag. The terminating step includes terminating the write operation on one of the two non-volatile memory cells according to the comparison flag. The write-back operating step includes performing a write-back operation on another of the two non-volatile memory cells.