Silico-ferrite of calcium and aluminum (SFCA) is a key bonding phase in high basicity sinter and its reducibility affects the reducibility of sinter. In this work, the reduction process of the Ca5Si2(Fe18−xAlx)O36 with change of aluminum content had been investigated using the thermogravimetric method at 1073 K, 1173 K and 1273 K in reducing atmosphere respectively. X-ray diffraction was used to characterize the mineral composition of the samples. Jade software was used to calculate the grain size of minerals and micro stain in samples. The results show that the reduction process of the SFCA to FeO could be divided into two steps, SFCA to Fe3O4 and Fe3O4 to FeO. Ca2Al2SiO7 as a by-product appeared in the stage of SFCA to Fe3O4. The increase of aluminum content in SFCA decreased the formation of Ca2Fe2O5 to promote the reducibility of SFCA at 1273 K. By calculation it was also found that the addition of aluminum resulted in more micro strain in the SFCA, which could deduced that the release of stress in the reduction process is also conducive to promote the reduction of SFCA.