Based on the analysis of the transmission of near infrared light in homogeneous tissues, a calculating method of diffuse reflection ratio (DRR) for layered tissue is presented. According to this method, the DRRs of two layers of tissues were calculated, which were consistent with former literatures. By use of this theoretical model, DRRs of two kinds of tissue with different structures are discussed. It shows that DRR of two-layered medium varies with detecting separation in the same tendency with that of former literature.