Abstract: Propagation of flat and Gaussian light beam in biological tissue is simulated with Monte-Carlo method. Through comparing the distribution of energy in biological tissue generated by single and multi-beam as well as flat and Gaussian light, influence of various light sources and the light spot size on the distribution of light absorption is analyzed. The results show that the laser energy is relatively concentrated while using Gaussian beam, but the lateral transport area is limited. Under the condition of the same total power, both large single beam and small multi-beam can enlarge the lateral area of the light propagation effectively, but the maximal light absorption rate increases for latter approach. For multi-beam combined sources, the distribution of light absorption is influenced by the distance between beams obviously.