Thermal interaction of bio-tissues laser heated presents sorts of thermal effects such as coagulation, vaporization, carbonization. Both the thermal effects and thermal damage produce due to the continuously accumulation and diffusion of the laser energy in tissue. Based on the analysis of the mechanism of the thermal propagation and equilibrium, the relationship among temperature rise, thermal damage and exposure duration was deeply discussed. With increasing of the laser energy and thermal source diffuse to the ambient tissue, the distribution of temperature rise changes from a shape δ function to normal function, the higher temperature makes the thermal damage to some extent. It is theoretically proved temperature rise is one of the most important factors in laser surgery. Clinically, with the shortage of the setup to trace the actual temperature of the target tissue, one is only to adjust the laser output or the duration time in order to get better curative effect, which could tend to bring excessive thermal damage or insufficient irradiation.