In this work, we suggested a method to evaluate quantitatively the effect of doping oxide on the phase coexistence of PbZr1-xTixO3 (PZT)-based ceramics through the analysis of the Raman scattering spectra. Theoretically, the degenerated T-3u mode in the cubic phase of PZT will transform as A(1)(3) and E(4) modes in the tetragonal phase or as rhombohedral (R) modes in the rhombohedral phase below the Curie temperature, which set up the theoretical base to study the phase coexistence in ferroelectric materials. Through separation by fitting of the Raman bands, the shifts and intensities of different Raman vibration modes were determined. A calculation equation representing the phase coexistence was put forward based on the theoretical analysis of the degenerated T-3u modes. The results showed that a turning point appears at the Fe2O3 addition of 0.3%. The variation in the electrical properties of the Fe2O3-doped Pb(Zn1/3Nb2/3)O-3 (PZN)-PZT ceramics also affirmed the turning point of the phase evolution as the addition of Fe2O3.