In order to study the propagation of near infrared light in the skin tissue, the human skin tissue model was established, including absorption coefficient, scattering coefficient, refractive index and anisotropy factor of epidermis, dermis and subcutaneous tissue in different incident wavelengths. Combining with the optical properties of skin tissue, the near infrared light propagation and distribution characteristics in skin tissue when subjected to different light source-detection distances from 1 000 nm to 1 900 nm were analyzed using Monte Carlo method. The results showed that photon path length and penetration depth increased with the increase of the source-detection distance, while normalized energy of diffuse light decreased with the increase of the source-detection distance. The source-detection distance was selected to be 0.45 mm. When the incident wavelength was 1 550 nm, the photon path length was 1.806 mm, the penetration depth was 0.467 mm, and normalized energy of diffuse light was 0.001 85. A kind of optical fiber detection structure was analyzed and designed according to Monte Carlo simulation results. The bifurcated fiber bundle was composed of 18 source fibers and 4 detection fibers, the distance of each fiber was 0.45 mm and just compactly adjacent. Finally, the diffuse light energy and illumination distribution collected by this optical fiber were simulated. Assuming that the incident light power was 1 W, the diffuse light power received by the detector was 0.598 mW. The results could provide a reference for the design of the portable detection spectra instrument.