During numerical simulation of laser and tissue thermal interaction, the light fluence rate distribution should be
formularized and constituted to the source term in the heat transfer equation. Usually the solution of light irradiative
transport equation is given in extreme conditions such as full absorption (Lambert-Beer Law), full scattering
(Lubelka-Munk theory), most scattering (Diffusion Approximation) et al. But in specific conditions, these solutions will
induce different errors. The usually used Monte Carlo simulation (MCS) is more universal and exact but has difficulty to
deal with dynamic parameter and fast simulation. Its area partition pattern has limits when applying FEM (finite element
method) to solve the bio-heat transfer partial differential coefficient equation. Laser heat source plots of above methods
showed much difference with MCS. In order to solve this problem, through analyzing different optical actions such as
reflection, scattering and absorption on the laser induced heat generation in bio-tissue, a new attempt was made out which
combined the modified beam broaden model and the diffusion approximation model. First the scattering coefficient was
replaced by reduced scattering coefficient in the beam broaden model, which is more reasonable when scattering was
treated as anisotropic scattering. Secondly the attenuation coefficient was replaced by effective attenuation coefficient in
scattering dominating turbid bio-tissue. The computation results of the modified method were compared with Monte Carlo
simulation and showed the model provided reasonable predictions of heat source term distribution than past methods.
Such a research is useful for explaining the physical characteristics of heat source in the heat transfer equation,
establishing effective photo-thermal model, and providing theory contrast for related laser medicine experiments.