It is highly necessary to study the phenomenon of photon migration in the knee joint for the non-invasive near-infrared optical early diagnosis of the osteoarthritis of the knee. We investigate the migration trace and distribution rule of the photons in knee layered structure, which are simulated by the Monte-Carlo modeling. The proportion of photons which collide with bone tissue then migrate out of the muscle tissue and photons directly migrate out of muscle tissue is calculated. For analyzing the signal-to-noise ratio to determine the accurate position of the detector, we perform quantitative evaluations of distribution of photons, as well as qualitative assessments of the distribution of photons.