Based on the laser ultrasonic method, the transmitted ultrasonic signals are monitored in real-time when the crack is irradiated with a heating laser and naturally cooled. Under the irradiation of different power heating laser, three typical processes of the crack wall asperities are obtained when the crack is closed by the irradiation of heating laser, and the causes of these different processes are analyzed and discussed. The results show that the change of crack under heating laser irradiation and natural cooling condition is related to the initial morphology characteristics of the crack when it is not heated.