Total knee arthroplasty is an effective method for treating knee diseases, but there is no unified view on the advantages and disadvantages of fixed-axis and mobile-axis knee prostheses. In the past, there have been comparative verifications of the two prostheses, but most of which are static simulations. In this paper, a finite element model of a healthy knee joint was built; then a knee joint containing the above two prostheses was established; finally, by dynamically simulating the knee flexion motion, the contact stress and contact area of the tibia-femoral joint were calculated. The results show that for the fixed and mobile axis artificial knee joints, in the range of 0° to 90° knee flexion angle, the contact area shifts from the front of the tibial liner to the rear, and the contact stress of the tibiofemoral joint continues to increase, reaching maximum at 90°. With respect to the fixed shafts, the contact pressure of the tibiofemoral joint between the moving shafts is smaller, and the contact area is larger. As the knee bending angle deepens, the contact stress on the polyethylene pads of the two prostheses gradually increases, and the contact area gradually decreases. No significant difference exists between the two prostheses in the contact stress, but there is a significant difference in the contact area of the two prostheses. The results suggest that under the same contact stress, the larger the contact area is, the less stress concentration is likely to happen, that is, the prosthesis is not prone to wear. This can extend the service life of the knee joint. Therefore, the mobile axis knee prosthesis is better than the fixed axis knee joint prosthesis. This study may provide a valuable reference for the selection of prosthesis transplantation types in clinic.