Al2O3-30vol%ZrO2 nano-submicron structured ceramics has been obtained from high-temperature melts produced by SHS metallurgical process, SEM images show that the multiphase ceramics is mainly composed of Al2O3 matrix eutecticums in which ZrO2 fibers are up to nano-submicron scale, resulting in formation of intra-granular structures. Vickers hardness test indicates that critical value of indentation load which induces median crack to extend is 30kg, and morphologies of Vickers indentation indicate that the ceramics is performed with high fracture toughness and high plasticity. Meanwhile, SEM images show that crack extension is mainly controlled by fiber eutecticums of intra-granular structures with nano-submicron ZrO2 phases, XRD demonstrates that toughening mechanism of stress induced ZrO2 phase transformation is considered weak through comparing volume fraction of m-ZrO2 before fracture to the one after fracture, and toughening behavior of multiphase ceramics is mainly controlled by nano-submicron phase toughening mechanism.