The positron annihilation lifetime spectroscopy, combined with X-ray diffraction and scanning electron microscopy is used to measure a new type of non-ferroelectric piezoelectricity SrTiO3-Bi12TiO20 (ST-BT) composite ceramic, which is prepared by conventional solid-state reaction in Shandong University. The structural characteristics and sinter process for ST-BT composite ceramic are systematically studied. A large number of crystal defects are observed in ST-BT composite ceramic with the sintering temperature being between 860 to 940 ℃. The large scale defects are formed due to the Bi12TiO20 phase decomposed when the sintering temperature rises to 980 ℃. The experimental results indicate that the structural characteristic and piezoelectricity of ST-BT composite ceramic shows good stability with the sintering temperature being between 920 to 940 ℃.