To satisfy the application of new type of metal alloy fuels in propellants and explosives, the spherical Al-Si alloy fuels with Si mass fraction of 12% and 20% were prepared by high-speed centrifugal atomization with absent-oxygen atmosphere. SEM, XRD, metallographic analysis were taken to study the structures and the constitutions of the alloys. Oxygen bomb calorimeter and TG-DSC were used to investigate the heat of combustion and thermal oxidation characteristics of the fuels. The morphologies and components of Al-20Si thermal oxidation products were tested in situ at 550, 620 , 1000 ℃ and 1200 ℃. Results show that the Al-Si particles are typical spherical, and core-shell structures. The shell is mainly formed from primary silicon and its particle size increases with an increased in the particle size of the alloy fuel. The cores is a three-dimensional structure of reticulated Si skeleton. The heat of combustion of Al-12Si is 29.285 kJ∙g^-1, and the mass of thermal oxidation reaction to 1200 ℃ is 51.17%. The heat of combustion of Al-20Si is 29.039 kJ∙g^-1, and the mass of thermal oxidation reaction to 1200 ℃ is 43.33%.