Objective To obtain the axial elastic modulus of rabbit articular cartilage based on the ultrasound swelling observation technique and the triphasic theory, and to explore the triphasic mechanical properties of the osteoarthritis cartilage with different pathological grades. Methods The articular cartilage samples from rabbit knees were assessed according to the different pathological grades. The swelling strains were recorded based on the high frequency transient ultrasound measurement technique. The axial elastic modulus of the cartilage samples was extracted based on the fixed charge density, the water volume fraction and the triphasic model. Correlation analysis was also made. Results There were both significant differences in axial elastic modulus between the normal cartilages and among the osteoarthritis cartilage with different pathological grades (P<0.05). The value of axial elastic modulus decreased with the increase of osteoarthritis grades. For normal cartilage samples, the average axial elastic modulus was (15.87±6.30) MPa. For osteoarthritis cartilages of grade 1, 2 and 3, the value of axial elastic modulus were (11.33±5.21), (9.15±5.68) and (6.05±4.99) MPa, respectively. Conclusions This study showed there are significant differences in triphasic mechanical properties of the articular cartilage with different osteoarthritis grades, which may provide some new thought for the quantitative assessment of osteoarthritis grade based on mechanical properties of cartilage.