Biomedical implants, such as the femoral head of total hip arthroplasty or the root of artificial teeth, are subjected to repeated loads in human fluid. As a result, the fatigue resistance and aging resistance of bioceramic implant are crucial to its long-term stability. Owing to the excellent strength and toughness of tetragonal zirconia polycrystals (TZPs) and their composites, they are now used as biomedical implants. Apart from strength and toughness, the capability to resist cyclic fatigue is also crucial. In the present study, the testing bar under 4-point bending and cyclic loading are used to evaluate the fatigue strength. The phase evolution of the specimen during fatigue is characterized using the XRD technique. The surface morphology of the tensile surface also reveals the characteristics of phase transformation behavior. The aging resistance is conducted in a hydrothermal environment. Though the monoclinic phase in the surface region increases with the increase of aging time, the depth with high density of flaws may not be observed using SEM. Through the use of TEM technique, the extent of phase transformation during aging can then be evaluated.