Abstract: Although fracture mechanics of polycrystalline alumiua has been intensively studied,the fracture mechanics property of single crystal alumina his not been reported to our best knowledge.In this study,We have been developing a ceramic heart valve using single crystal alumina,due to its superior anti-thrombus ability. We measured the fracture toughness of two batches 10 single crystal alumina specimens,demonstrated the three dimensionwl model of single crystal ceramic crack growth.Scanning electron microscopy was used to examine the fracture surfaces of she specimens.The fracture micro-mechaniwm of ceramic was explained.The way of increrssing toughness of composite of ceramic matrix was disclosed.