The combustion synthesis (self-propagating high-temperature synthesis, SHS) of a model Cr-CrO3 system is studied both experimentally and theoretically. The system is chemically simple, i.e. it is composed of only two elements, and convenient for combustion and phase formation studies. A new combustion model for a "metal-metal oxide" system and a mathematical model of phase and structure formation are developed. A number of dependencies are determined in the experiments and are described in the combustion model. It is shown that the leading combustion stage is the gas phase oxidation reaction. Different types of microstructures formed from homogeneous melt are revealed. A qualitative agreement between experimental data, theoretical analysis and calculation results is obtained.