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BACKGROUND: The mechanical environment of cartilage with osteoarthritis at all levels has a certain influence on the development of osteoarthritis. Computer simulation provides a method to quantify the mechanical environment of knee joint cartilage, which makes it possible to study the mechanical behavior of osteoarthritis cartilage by finite element method. OBJECTIVE: To study the stress distribution of cartilage and the change rule of fluid velocity in cartilage of healthy adults and cartilage with osteoarthritis at all levels through numerical simulation so as to explore the mechanical behaviors of cartilage with osteoarthritis at gait cycle. METHODS: The knee joint data of healthy adults were obtained by CT and MRI scanning, and the three-dimensional finite element model of the whole knee joint was established by Abaqus software. The software HyperMesh was used to divide the mesh of the total knee joint, and the binding relationship and interaction between internal components of the knee was set. By changing the material properties of cartilage and adjusting the time length of each phase and the angle between femur and tibial plateau, the cartilage load and boundary conditions of healthy adults and osteoarthritis at all levels could be set in the model. RESULTS AND CONCLUSION: (1) The simulation results showed that the mean Mises stress and the change curves of fluid velocity in the femur cartilage and tibia cartilage increased firstly and then decreased in the gait cycle. (2) Compared with healthy adults, the Mises stress of cartilage in patients with osteoarthritis at all levels continually decreased with duration of disease. The flow velocity of fluid in cartilage firstly increased and then decreased when it developed to osteoarthritis grade 3, and the change range of Mises stress and fluid flow velocity of cartilage with osteoarthritis at all levels decreased. (3) Therefore, with the continuous development of osteoarthritis, the fluid flow velocity increased, the Mises stress decreased and the range of joint surface stress changes decreased in a gait cycle, which lead to the weakening of joint bearing and cushioning capacity. [ABSTRACT FROM AUTHOR]