Bionic knee was important basic driving element for biped robot. with the adult male's right leg knee working as bionic prototype, the three-dimensional finite element model wes established, and the cinnections balance equation was established with the help of nonlinear contact theory, then system penalty function was used to deal with the contact constraint by considering the minimum potential energy under the restriction of weight load conditions. further, the biomechanical response and shock buffering function of sagittal knee with cartilage was analysed, and the constraint stress mechanism of articular cartilage between the sagittal knee with and without cartilage was compared. the comparative analysis would offer biomechanics basis for bionic joint drive's optimal design.