To understand the oxidation mechanisms of (TiC+TiB+(TiZr)5Si3)/TA15 composites and elucidate their superior oxidation resistance, a systematically microstructural characterization of the oxide scale was investigated. The results showed that the oxide scale was consisted of the outer R-TiO2+Al2O3 mixed layer, inner gradient R-TiO2 layer, dispersive amorphous/nanocrystalline SiO2 and interfacial Ti2AlN+Ti2N layer. Such multi-layered structure could efficiently hinder the penetration of oxygen and alleviate the thermal stress generated during cyclic oxidation. Moreover, the thermodynamic stabilities of different Ti-O compounds were calculated by the first principles method, which revealed the evolution of Ti-O compounds.