InSe is a typical two-dimensional (2D) layered semiconductor material, which has excellent electrical properties and moderate adjustable band gap. It is found that InSe has an attractive application prospect in optoelectronic devices. However, some studies have shown that InSe in a single selenium vacancy (Vse) system is easily degraded when exposed to the environment of O₂ molecule, which seriously affects the application of InSe in the field of electronic devices. In order to improve the environmental stability of the material, the substitution doping method of Te is proposed in this work. Density functional theory (DFT) is used to analyze the electronic structure, adsorption energy, Bader charge and energy reaction paths of the different systems. It is found that Te substitution doping can significantly improve the stability of InSe. At the same time, the defect state produced by Vse can be eliminated. The specific research results are as follows. First, the dissociation barrier of O₂ molecule on Te doped InSe surface (InSe—Te) is as high as 2.67 eV, indicating that Te-doped InSe has a strong antioxidant capacity. Second, the distance between O₂ molecule and the surface of InSe—Te is 3.87 Å, and the adsorption energy is only –0.03 eV, indicating that O₂ molecules are physically adsorbed on the monolayer surface. Third, Te doping not only improves the antioxidant capacity of the InSe, but also eliminates the defect state produced by Vse. Fourth, the Te-doping obviously eliminates the original Vse defect state or impurity band. The density of states and band structure of Te-doped InSe are almost the same as those of perfect InSe, which can maintain the stability of InSe structure and effectively reduce the damage of oxidation environment to defective InSe monolayer. The results of this study will be helpful in improving the environmental stability of InSe 2D material devices and promoting the research and development of InSe 2D devices.