Multi-component solid solutions with non-stoichiometric compositions are characteristics of ultra-high temperature carbides as promising materials for hypersonic vehicles. However, for group IV transition-metal carbides, the oxidation behavior of multi-component non-stoichiometric (Zr,Hf,Ti)C_x carbide solid solution has not been clarified yet. The present work fabricated four kinds of (Zr,Hf,Ti)C_x carbide solid solution powders by free-pressureless spark plasma sintering to investigate the oxidation behavior of (Zr,Hf,Ti)C_x in air. The effects of metallic atom composition on oxidation resistance were examined. The results indicate that the oxidation kinetics of (Zr,Hf,Ti)C_x are composition dependent. A high Hf content in (Zr,Hf,Ti)C_x was beneficial to form an amorphous Zr-Hf-Ti-C-O oxycarbide layer as an oxygen barrier to enhance the initial oxidation resistance. Meanwhile, an equiatomic ratio of metallic atoms reduced the growth rate of (Zr,Hf,Ti)O₂ oxide, increasing its phase stability at high temperatures, which improved the oxidation activation energy of (Zr,Hf,Ti)C_x.