Optical coherence tomography (OCT) is a noninvasive cross-sectional imaging modality capable of measuring tissue morphology and function with high spatial resolution. Both the amplitude and the phase of the interometric heterodyne signal can be exploited to obtain the profile of sample reflectivity related to its microstructure and the bi-directional blood flowing velocity information. The fact that the skin and human mucosa have a layer structure suggests that the backscattered signal from tissue arises from two sources. The first is the scattering particles within the tissue. The second is the Fresnel refraction on the interface between two layers. However, the analysis available only considers one aspect of the backscattering sources. In this paper, we report an analysis that is based on the combination of both the particle scattering within the tissue and the Fresnel reflection on the interfaces between two layers. The new model is more reasonable for establishing the relationship between the signal detected by OCT scanner and tissue structures.