Total time-resolved reflectance calculated based on the diffusion theory with zero-boundary conduction(ZBC) and extrapolated-boundary conduction(EBC) in semi-infinite biological tissue are compared with Monte Carlo simulations.The corresponding diffusion equations are fitted to Monte Carlo simulations data for determining the optical parameters of tissues.It is shown that the errors in the absorption coefficients derived from two the diffusion models are smaller than 10 %,the errors in reduce scattering coefficients derived from the diffusion model with EBC relate to the optical parameters of tissues,whereas,the errors in reduce scattering coefficients are large for different optical parameters when ZBC is used.