Calcia stabilized zirconia(CSZ) ceramics were prepared with 7wt% calcia-stabilized zirconia powder by pressureless sintering technology. The crystal phases of the sintered samples were studied by X-ray diffraction(XRD) and Raman spectroscopy techniques, and the microstructures of the fracture surfaces were observed by scanning electron spectroscopy(SEM). The phase compositions and the lattice parameters of cubic calcia-stabilized zirconia were calculated by XRD patterns. As the sintering temperature increasing from 1400 ℃ to 1600 ℃, the monoclinic zirconia content decreases gradually, finally all monoclinic phase transforms to cubic calcia-stabilized zirconia, which is deter-mined to be Ca0.134Zr0.866O1.866. It is revealed that monoclinic zirconia is the main factor causing minute cracks on the surface of sintered samples, and the combination of the XRD patterns and Raman spectra is an effective way to research the phase transformations of zirconia.