The size of alumina inclusions in steel seriously affects its performance. Refinement or removal of these inclusions is highly valued. Because the size of inclusions in molten steel is relatively small and errors occur in the analysis process, the idea of amplifying the inclusion reaction was implemented to study the effect of different proportions of rare earth cerium oxide and alumina powder at a high temperature of 1 600 ℃ on the inclusion phase change and size. A high-temperature box-type furnace was heated, the temperature was maintained, and the furnace was subsequently cool. According to the test results, the specific change process of cerium aluminum oxide was examined. An energy spectrum analyzer, X-ray diffractometer, X-ray fluorescence spectroscopy instrument, and Raman spectrometer were employed to target inclusion changes specifically. The results show that with an increasing amount of alumina added, the phase of the product during the powder sintering process changed from +4 valence rare earth oxide to +3 valence rare earth oxide. According to the XRD pattern, the CeAlO3 phase was first generated, followed by the characteristic peak strength of the CeAlO3 phase gradually diminishing and disappearing, which was replaced by the CeAl11O18 phase. The XRD peak broadened, the characteristic peak weakened, the half-height width increased, the grain size decreased, and the crystallinity was reduced. Combined with three mathematical models of the average grain size, namely, D-S, W-H and H-W, R2 was calculated to be 0.761 78, 0.971 01, 0.920 81, and 0.961 87; and 0.989 65, 0.988 01, 0.978 42, and 0.981 28. The comparison reveals that the H-W method results exhibit a better fit, and the grain size of samples 4# to 1# gradually decreased to 7.63, 6.27, 5.99 and 3.97 μm, indicating that the increase in rare earth cerium could promote nucleation and reduce the grain size. By analysing the Raman spectra, as the phase fraction of Al2O3 increased, the Raman peak intensity from 464～465 cm-1 gradually weakened until it disappeared, and it was deduced that the phase was a ceria phase. The Raman intensity at a displacement from 4 351～4 399 cm-1 gradually increased, and combined with the XRD pattern. It could be determined that the substance was CeAl11O18. The obtained change rule is consistent with that determined by XRD. By enhancing the substances in steel requiring targeted research, the evolution process of alumina powder products after the addition of ceria powder is analyzed. The research results provide a reference to resolve the problem of alumina inclusion modification in steel.