The adsorption behaviors of intrinsic graphene-like GaN (g-GaN) and transition metal (TM) atom-doped g-GaN on Cl₂ and CO gas molecules were systematically investigated using first-principles calculations based on density functional theory. The results show that the adsorption of both Cl₂ and CO on the intrinsic g-GaN was physisorbed, and since the adsorption energies of both systems were positive, it indicates that the systems are unstable. On the contrary, the adsorption energies of Cl₂ and CO upon adsorption on Fe- and Co-doped g-GaN were negative and small, and the adsorption system is stable. By analyzing the properties of the density of states, charge density difference, and energy band structure, it can be concluded that the introduction of transition metal atoms can effectively enhance the interaction between gas molecules and g-GaN.