A tissue is multi-layered mismatched medium, but many investigators only study the diffusion equation of matched medium, they take the tissue as media with the same refractive index. In order to understand the light transport in tissue, the solution of the diffusion equation of a three-layered mismatched medium in frequency domain is set up. Through Fourier transform, the time-resolved reflectance is computed. The time-resolved reflectance between the solution of three-layered mismatched media diffusion equation and Monte-Carlo simulation are compared. The result shows the method not only accords with the Monte-Carlo simulation, but also can solve the problem of a two-layered mismatched turbid media model.