A two-dimensional mathematical model was developed to simulate the photo-thermal interaction of biological tissue subjected to the surface-applied laser irradiation.Laser energy deposition in biological tissue was simulated using Monte Carlo method and temperature distributions in tissue were then numerically calculated using finite difference method based on the Pennes bioheat equation.The numerical results show that the temperature increase will be overestimated if thermal properties of tissue are assumed to be constant as most current researchers take.Moreover when laser energy deposition is assumed to be the specific exponential function temperature increase in tissue near the light spot was much higher than the corresponding value when Monte Carlo method was used to simulate laser energy transport.Under the same operating conditions that tissue temperature increase near light spot becomes smaller and influenced region where tissue temperature increased perceptibly bocames larger with the 1/e~2 radius of laser beam increased.