Al

2

O

3

-Cr and Al

2

O

3

-（Cr

2

O

3

）-Cr ceramic matrix composites were successfully prepared in ceramic mold and graphite mold by combustion synthesis.The effects of Al

2

O

3

and Cr

2

O

3

dilutor on initial reaction temperature and adiabatic temperature were investigated by thermodynamic calculation.It was found that the dilutor can improve initial reaction temperature and decrease adiabatic temperature.Al

2

O

3

and Al

2

O

3

- Cr

2

O

3

solid solution matrix composites can be prepared by changing the dilutor proportion

in which with proper dilutor

fine Cr phase with sub-micron size can be uniformly distributed in the Al

2

O

3

matrix.The uniformity and fineness of microstructure of the composites in graphite mold are superior to those of in ceramic mold.