Objective To investigate the compressive relaxation behavior of cartilage in different regions of the knee joint at different strain rates, and construct the viscoelastic mechanics of cartilage in each region, so as to provide a reference for the prevention of cartilage-related diseases and the development of cartilage repair materials. Methods The knee cartilage of beagle dogs was regionally divided, and the uniaxial unconfined compressive relaxation properties of cartilage in each region were tested by a universal testing machine at different strain rates, and the constitutive models were constructed. Results The cartilage exhibited a notable stress attenuation. Furthermore, the normalized stress reduction increased significantly with increasing strain rate. For cartilage in lateral plateaus of tibia, the normalized stress reduction at strain rate 5×10-4 s-1 was 19%, and increased to 69% at strain rate 5×10-2 s-1. The relaxation equilibrium stress remained relatively constant at all strain rates. The Ogden-Prony viscoelastic model of cartilage in each region was developed with a goodness of fit R2>0.98. Conclusions The knee cartilage demonstrates a significant viscoelastic response in relaxation tests, exhibiting the rate-dependent and region-dependent properties. The Ogden-Pony viscoelastic model can reflect the strain rate-dependent stress relaxation behavior of cartilage.