Autofluorescence characteristics of Basal Cell Carcinoma skin were studied by Monte Carlo method. Based on the microscopic autofluorescence image, an eight-layered optical model of skin Basal Cell Carcinoma was constructed. By Monte Carlo simulation, the light distribution in the model was calculated, and the diffuse reflectance process was modeled in visible wavelength range in order to perfect the multi-layer tissues optics model. Monte Carlo method was used to simulate the tissues reabsorbtion and rescattering effect on intrinsic autofluorescence based on the light-tissue interactions. The escaping process of autofluorescence photons from tissue surface was discussed, and the in vivo autofluoresconce spectra of skin Basal Cell Carcinoma were reconstructed. The results show that the rebuilted skin autofluorescence spectra achieve a good agreement with the experimental results. This study will provide a practical theoretical method to study transmission process of intrinsic autofluorescence in skin cancer lesions, and revealed autofluorescence characteristics of skin cancer.