The effect of additives for reducing the olefins in the fluid catalytic cracking gasoline was studied in the micro-fixed bed reactor, and the rare-earth Ce was supported on the magnesia - alumina spinel additive. From the X-ray diffraction spectra, it was found that the form of the spinel was suppressed and that different crystal forms were formed with different activation temperatures. The effect of Ce4+ for reducing the olefins is better than that of Ce3+.