Abstract: By using the combustion synthesis under high gravity and adjusting the volume fraction of ZrO₂，ZrO₂(4Y)/Al₂O₃ composite ceramics with different compositions and micro-structural morphologies were prepared，and the correlations of the composition，microstructures and mechanical properties of the materials were investigated. The results of XRD，SEM and EDS show that as the volume fraction of ZrO₂ is below 37%，the ceramic matrix grows from the melts to be the random-orientated rod-shaped colonies，of which the submicron-meter fibers of tetragonal ZrO₂ are orderly embedded in the α- Al₂O₃. As the volume fraction of ZrO₂ is above 40%，the ceramic matrix develops to be the tetragonal ZrO₂ grains which are shaped like spheres. The results of mechanical properties indicate that the relative density of the ceramics decreases with increasing the volume fraction of ZrO₂，the hardness and fracture toughness of the ceramics simultaneously have the maximum values as the volume fraction of ZrO₂ is 33%，and the bending strength of the materials has the maximum value as the volume fraction of ZrO₂ is 29%.