With the continuous emission of greenhouse gases, the greenhouse effect is becoming more and more serious. CO₂, CH₄, and N₂O are three typical greenhouse gases, and in order to limit their emissions, it is imperative that they are accurately monitored. In this paper, the doping behavior of Ti on the surface of HfSe₂ is investigated, based on the first-nature principle. Additionally, the parameters of adsorption energy and the transfer charges of Ti−HfSe₂ for CO₂, CH₄, and N₂O are calculated and compared, while the sensing characteristics of Ti−HfSe₂ are analyzed. The results show that the structure is most stable when Ti is located above the lower-layer Se atom. The CO₂ and N₂O adsorption systems with large adsorption energies and transfer charges are a chemical adsorption, while the CH₄ system is a physical adsorption with small adsorption energies and transfer charges. In addition, Ti−HfSe₂ has a good sensitivity and recovery time for CO₂ at 298 K, which is feasible for industrial application. All the contents of this paper provide theoretical guidance for the implementation of Ti−HfSe₂ as a gas-sensitive material for the detection of greenhouse gas components.