The oxidation resistance plays an important role in high-temperature ceramics. Although transition metal sili-cides exhibit the better oxidation behavior, the improvement of oxidation resistance is still a great challenge for their applications. Here, we apply first-principles calculations to investigate the oxidation mechanism and the influence of alloying elements (Cr and Al) on the oxidation resistance of Nb3Si(111) surface. The calculated results show that the O atom is adsorbed on the Nb-Si-bridge site because of the charge interaction between O-2p state, Si-3p state and Nb-4d state. We further find that Cr-doping is more thermodynamically stable than that of Al-doping. In particular, the capacity of oxidation resistance follows the order of Cr > Al > Si. Finally, we conclude that Cr-doping can effectively improve the oxidation resistance of Nb3Si(111) surface. The calculated electronic structure shows that Cr d-orbital plays a crucial role in oxidation resistance.