The　femtosecond　laser-driven　ultrafast　evolution　of　free　carriers　during　the　phase-change　process　of　N-doped　Ge2Sb2Te5　(N-GST)　film　was　studied　in　this　paper.　And　mechanism　of　initial　absorption　peak　was　calculated　by　two-temperature　model.　We　found　that　the　formation　of　Ge-N　weaken　the　initial　optical　absorbance　and　decreased　the　concentration　of　free　carriers,　then　improved　the　temperature　of　crystallization　in　N-GST.　The　doping(N)　can　reduce　the　grain　size　because　of　the　easing　of　optical　energy　absorbance.　At　last,　we　inferred　that,　if　the　incident　laser　fluence　is　enough　for　phase　transformation　point,　the　transformation　velocity　of　N-doped　GST　is　faster　than　GST.　©　Published　under　licence　by　IOP　Publishing　Ltd.