When ClO2 is exposed to heat, light, organic matter, or other environments that promote oxidation, it can rapidly decompose and can even cause an explosion; therefore, its physical and chemical decomposition has a wide range of implications. Herein, density functional theory is used to examine the adsorption of ClO2, HCl, HClO, and Cl2 on single‐vacancy‐, double‐vacancy‐, and Stone–Wales‐defected graphene and metal (Fe or Au)‐doped graphene to verify their effects on the adsorption of the target gases. Specifically, the adsorption energy, charge transfer, density of states, and charge density differences in the adsorption systems are investigated. The results indicate that the target gases are strongly adsorbed on metal‐doped graphene, particularly when doped with Fe. In contrast, the interactions between defective graphene and the adsorbed gases are weaker. However, single‐vacancy‐defected graphene also has better performance for the adsorption of target gases. This study provides a theoretical basis for the development of sensitive gas sensors for ClO2 and its decomposition products and is expected to guide further research on modified graphene‐based gas sensors.