It was demonstrated experimentally that doping Zr into TiAlN coatings at room temperature will detriment its oxidation resistance. On the other hand, there are evidences that doping Zr into TiAlN at high temperature will improve coating's oxidation resistance. In the present work, we address the effect of Zr on the oxidation resistance of TiAlN by means of ab initio molecular dynamics simulations. The TiAlN and TiAlZrN (1 Zr atom replacing 1 Ti atom) surfaces covered with 4 oxygen atoms at 300 K and 1123 K were simulated. Based on the analysis of the atomic motion, bond formation after relaxation, and the charge density difference maps we find that at 300K, the addition of Zr induces escape of Ti atoms from the surface, resulting in formation of surface vacancies and subsequently TiO2. Comparison of metal oxygen dimers in the vacuum and above the TiAlZrN surface further shows that the addition of Zr in the TiAlN surface will change the lowest bonding energy sequence from Zr O < Ti-O < Al-O in the vacuum to Ti O < Zr O < Al-O above the TiAlZrN surface. From Molecular Dynamics simulations at 1123 K, it is find that no Ti vacancies were generated in the surface. Moreover, less charge is transferred from metal to N atoms and the bond lengths between Ti and 0 atoms become shorter at 1123 K as compared with 300K, suggesting that the addition of Zr atom promotes the interaction of Ti and 0 at TiAlZrN surface at 1123 K, leading to a more stable surface. Our simulation explains why Zr-doping at 1123 K increases TiAlN coating's oxidation resistance while at 300 K reduces its oxidation resistance. (C) 2016 Elsevier B.V. All rights reserved.