A 3-D finite element model, including cartilages, menisci and four main ligaments, was developed to investigate the effect of anterior cruciate ligament (ACL) injury on the biomechanics of knee joint. The menisci were assumed to be transversely isotropic and ligaments to be hyperelastic. The biomechanics of tibiofemoral joint were analyzed under 134 N posterior femoral force in three cases, corresponding to intact, 1/3 injured and 2/3 injured ACL. It was found that the highest Mises stress in menisci moved from lateral meniscus to medial meniscus with ACL damage aggravating, which corresponded to the clinical symptom that medial meniscus injury often...