Transient　temperature　field　of　GaN　material　irradiated　by　pulse　laser　with　different　energy　density　was　simulated　and　analyzed　for　Al2O3/GaN　laser　lift-off　technique　using　the　finite　element　method　(FEM).　Al2O3/GaN　lift-off　experiment　has　also　been　carried　out　using　248-nm　KrF　excimer　laser.　The　simulated　results　using　FEM　were　consistent　well　with　experiment　results.　It　was　found　that　for　the　certain　laser　source,　the　temperature　varied　quickly　with　time　and　depth　in　GaN　material,　and　the　energy　density　of　pulse　laser　should　be　no　less　than　the　threshold　energy　density　in　order　to　realize　lift-off　successfully　and　no　more　than　the　maximum　value　for　avoiding　damage　caused　by　too　high　temperature.　During　multi-pulse　laser　processing,　another　key　parameter　was　pulse　frequency,　whose　variation　range　was　calculated　as　the　function　of　the　energy　density　of　laser.