The process of laser lift-off of GaN thin films from substrates was analysed.A temperature distribution analytical calculation form of the GaN/Al_2O_3 material irradiated by pulsed laser was presented under one dimension,and the temperature calculation form of different interface was obtained.The results show that the temperature of interface is in proportion to the square root of time when the material is irradiated by single pulse laser,however,it increases saw-like when the material is irradiated by continuous pulse laser.