Using tresh cadaveric knee jiont specimens, the author makes systematic experimental researcheson the ligament viscoelasticity property of the anterior cruciate ligament and its replacements thepatellar ligament and the illiotibial tract. The author establishes the viscoelasticity mechanicalmodel,deduces the constitute equation of the anterior cruciate ligament, the patellar ligament andilliotibial tract, makes systematic analyses of the creep and loose phenomenon of the ligament. Theresults indicate that ligament failure is connected with its biomechanical properties, theviscoelasticity property of patellar ligament is more like that of the anterior cruciate ligament, theintra-articular substitution using the patellar ligament is better than using illiotibial tract.