In order to compare laser lift-off thermal conductive effects by nanosecond laser and picosecond laser in GaN on AlN of micro light-emitting diode(micro-LED), an improved theoretical model of laser lift-off process for real-time ultraviolet light absorption and heat conduction was established. This model was used to calculate and analysis the thermal field distribution of GaN materials irradiated by various ultraviolet, laser pulses with different laser wavelength, laser pulse width, laser energy density. And the threshold conditions suitable for micro-LED devices of laser lift-off process by nanosecond laser and picosecond laser were obtained. The results show that laser pulse width, laser wavelength, and laser energy density are the key factors of laser lift-off process. The suitable laser wavelength includes 209 nm~365 nm ultraviolet band, and the laser lift-off effect of picosecond laser is better than that of nanosecond laser. Moreover, the shorter the pulse width and the shorter the wavelength of laser, the lower the threshold energy of laser pulse is needed for lift-off, and the smaller the thermal impact on the LED chip area. This research provides an important reference for the development of new laser lift-off equipment and related process applications.