Human knee joints can support high levels of mechanical load for decades. The mechanical factor plays an important role in the development of osteoarthritis of the knee that interferes to daily life. It is recognized that the morphological change due to the injury or thinning of meniscus may influence the mechanical environment of the knee cartilage and meniscus. To investigate the effects of the thinning of meniscus three dimensional finite element models of two knee joints the normal one and the one with thinning of the meniscus were constructed from the medical images and the finite element contact analysis of the knee joint was carried out in the present study. The load condition during level walking was introduced in the analysis. The results show that the stress magnitude and the location with the highest contact stress in the tibial cartilage are different in the two models. The higher stress and larger deformation were observed in the knee joint with thinning of meniscus.