We　demonstrate　ultrafast　amorphization　in　a　Ge2Sb2Te5　(GST)　film　through　a　nonthermal　process　by　femtosecond　pump-probe　experiments.　A　strong　absorption　peak　in　532　nm　is　founded　during　the　amorphization　and　the　energy　level　corresponded　is　about　0.65∼3.82　eV　by　calculations.　First-Principles　Calculations　simulation　experiments　are　used　to　prove　the　results　of　experiment　and　then　explain　the　mechanism　of　amorphization　of　GST.　Also,　results　of　experiments　show　that　the　time　to　reach　the　absorption　peak　is　decided　by　pulse　width　and　wavelength　but　not　the　laser　influence.　©　Published　under　licence　by　IOP　Publishing　Ltd.