An operation method of a non-volatile memory suitable for a multi-level cell having a first storage position and a second storage position is provided. The operation method includes: setting N threshold-voltage distribution curves, wherein the N threshold-voltage distribution curves correspond to N levels and N is an integer greater than 2; programming the first and the second storage positions to the 1st level and an auxiliary level respectively according to the 1st threshold-voltage distribution curve and a threshold-voltage auxiliary curve when the first and the second storage positions are programmed to the 1st and Nth levels; and programming the first and the second storage positions to the ith level according to the ith threshold-voltage distribution curve when the first and the second storage positions are not to be programmed to the 1st and Nth levels, wherein i is an integer and 1≦i≦N.