As is well known, the leakage of four toxic gases, NO ₂, NH ₃, mustard gas and sarin greatly threaten the environment and human health. Among of them, mustard gas and sarin are two serious chemical and biological weapons agents, and exposure to a small amount can cause skin burns and immediate death. NO ₂and NH ₃are two common toxic pollutants produced by automobile exhaust, coal combustion and petrochemical industry. The presence of trace amounts of NO ₂and NH ₃gas in human tissues can cause serious respiratory diseases and damage human brain and other systems. Thus, it is very important to realize the rapid detection of NO ₂, NH ₃, mustard gas and sarin in academia and industry. In this study, we use density functional theory to investigate the ability of a transition metal Mo doped two-dimensional VS ₂structure to detect the four representative toxic gases. The results reveal that Mo atom doping has a significant effect on the stability and gas-sensitivity of the VS ₂structure. The Mo atom can be successfully doped on the S-vacancy in the two-dimensional VS ₂structure. Compared with the undoped structure VS ₂, the doped structure Mo-VS ₂has strong interaction with NO ₂, NH ₃, sarin, and mustard gas, realizing effective adsorption of them. The presence of Mo atom in the VS ₂lattice changes the electronic structure of VS ₂, also modifies its band gap and density of states. The interaction between the Mo-VS ₂structure and the target analytes depends strongly on the nature of the gas molecule. The binding energy values for NO ₂, NH ₃, mustard gas, and sarin on the Mo-VS ₂are significantly higher than those on the pristine VS ₂, indicating stronger interaction between the Mo-VS ₂structure and these gases. Our calculations show that the Mo atom in VS ₂changes its electrical resistance after being exposed to the gases, which can be used to distinguish different gases. Moreover, differences in charge redistribution within the Mo-VS ₂structure upon being exposed to different gases can be used to explain their differential gas-sensitivity. Our results can provide sufficient theoretical basis for experimental researchers to design and optimize the performances of sensors in practical applications.