The main components were selected based on SiO₂-Al₂O₃-ZrO₂ (SAZ) phase diagram. Under 1700℃, the homogenous full-density amorphous bulk was obtained. The Si-Al-Zr-O composite ceramics with ultra fine grains were obtained via the given heat treatment processing. The effects of heat treatment processing on the crystallization process of the Si-Al-Zr-O amorphous bulk were analyzed with the aid of differential scanning calorimetric (DSC), X-ray diffraction (XRD)，infrared spectra (IR) and scanning electron microscopy (SEM). The results show that the crystallization of SAZ amorphous bulk begins at about 950℃ and completes at about 1150℃. The main phases are mullite, zirconia. The additions of ZrO₂, TiO₂ are useful to improve the crystallization behavior. With the content of ZrO₂ increasing, the t-ZrO₂ and mullite crystallization temperatures are decreased. The existence of ZrO₂ can decrease the activation energy of mullite effectively. In addition, with the increase of the heat treatment temperatures, the crystallized grains grow rapidly from 40 nm to 1 μm. Consequently, the transformation of Zirconia from tetragonal into monoclinic will be induced.