Abstract: The properties of YA-TZP depend on its microstructures. Optimal combination of mechanical properties with σ_b =940~1010 MPa and K_1c=10.9 MPa√m was obtained as the critical grain size~0,7μm. No strength degradation after aging at 250℃ for 50h. The morphology of different phases in ZrO₂, the microcracks and particles of secondary phase wereinvestigated and dislocation networks and lines were found under TEM. Pre-liminary tests show good prospect on application for wire drawing dies.