Objective To study the distribution of stress, strain and effective surface pressure in the knee joint. Methods Based on CT/MR scan image data and using the Mimics/ANSYS software, a three-dimensional finite element model of the knee joint (including the upper/lower knee and the meniscus) was established with the principle of reverse engineering, and the treatment of articular cartilage and ligament was ignored in this model. The mechanical responses of the three models, i.e., the healthy knee joint, the knee joint with V-shape medial meniscal tears, the knee joint with longitudinal meniscal tears under axial loading were analyzed and compared. Results Under axial loading, the healthy knee joint would transfer the majority of the compressive stress loads, which were mainly concentrated in the lateral side of the middle part of the meniscus, and the maximum contact pressure appeared in the rear area of the middle part of the meniscus. When the meniscus was torn, the maximum stress appeared at the periphery of the tear, and the contact stress distribution of the meniscus was significantly changed due to the presence of the tear. Conclusions The meniscal tears have a significant influence on the stress distribution and peak stress of the knee joint. According to the shape of the meniscus, the doctor can determine the position of the stress concentration in the meniscus, and to determine the most important point in the treatment of the meniscus tear.