Objective To study the mechanical response of tibial prostheses and the distal tibial cancellous bone after implantation of radial and axial functionally graded materials (FGM) into the ankle joint. Methods Three FGM were used: titanium alloy-bioactive glass composite FGM (FGM-I), titanium (Ti) alloy-ideal bone elastic composite FGM (FGM-II), and Ti alloy-hydroxylapatite composite FGM (FGM-III). A three-dimensional finite element model of total ankle arthroplasty (TAA) was established, and the simulation software ABAQUS was used for secondary development based on Fortra. By changing the volume fraction, the mechanical properties of the FGM tibial prosthesis can be adjusted both axially and radially. The stress distributions of the tibial prosthesis and cancellous bone after FGM axial and radial tibial component implantation in the standing position were analyzed. Results Compared with Ti alloy tibial prosthesis, three kinds of FGM could effectively reduce the stress concentration on the tibial prosthesis, and the overall effect of FGM-III tibial prosthesis was better than that of FGM-I and FGM-II tibial prosthesis; the radial distribution of FGM could effectively reduce the maximum von Mises stress of the prosthesis. For the tibial cancellous bone, the three types of FGM radial tibial prostheses and FGM-III axial tibial prostheses could effectively increase the distal stress, thus, relieving the stress shielding on the cancellous bone; the FGM-III radial tibial prosthesis was the most effective in improving the stress level of the cancellous bone. Conclusions FGM-III radial ankle prosthesis can effectively reduce the stress concentration phenomenon and the stress shielding effect on the prosthesis to prolong its life, with potential application prospects.