Near－IR radiation is often utilized to detect the p roperties in tissues. Up to now, a semi－infinite media photon migration model and a two－layered turbid medium model are utilized widely. But actually, there is a multi－layered turbid medium in tissue. In the paper,According to the diffusion equation, emp loying the extrapolated boundary condition,we analyze the diffusion of photons of a four－layered matched medium and deduce the solution of Green’s function. Through comparing the spatially resolved reflectance between the solution of four－layeredmatchedmedia diffusion equation andMonte－Carle simulation,we find our solution of a four - layered matched media theory not only accord with a two－layered turbid medium modelwhich is solved by A. Kienle, but also accord withMonte－Carlo simulation.