Articular surface conformity is a critical factor influencing the biomechanics of knee prostheses, yet its impact on the biomechanics of rotation-hinged knee (RHK) prostheses and their tibial fixation remains unclear. In this study, a rotational platform tibial insert model of RHK prostheses with varying coronal and sagittal conformities is established. Finite element analysis was performed under ISO boundary conditions to investigate the effects of articular surface conformity on the biomechanics of the RHK prosthesis and tibial fixation. The study revealed that when the coronal conformity decreased from 0.83 to 0.33, the maximum Mises stress in the tibia and the maximum contact pressure in the insert increased by 10.78% and 52.62%, respectively, while the maximum shear stress in the bone cement decreased by 10.17%. When sagittal conformity decreased from 0.88 to 0.47, the maximum Mises stress in the tibia and maximum contact pressure in the insert increased by 5.62% and 14.31%, respectively, while Mises stress at the hinge-rotation axis and bone cement shear stress decreased by 62.53% and 29.46%, respectively. A reduction in conformity decreased the contact area. Sagittal conformity has a lesser impact on insert contact pressure compared to coronal conformity, but a more significant impact on bone cement shear stress, and reducing sagittal conformity could effectively reduce the Mises stress at the hinge-rotation axis. The coronal conformity of the RHK prosthesis on the rotational platform more effectively regulates contact mechanics, reducing sagittal conformity facilitates lowering hinge-rotation axis Mises stress and bone cement shear stress without significantly increasing contact pressure, thereby mitigating risks of prosthesis failure such as dislocation, fracture, and loosening.