The stable geometry, electronic property and chemical reactivity of dopants (Co, Mo and B) incorporated N4 centers in graphene sheets (D-GN4) are investigated using the first-principles calculations. It is found that the GN4 sheet can strongly stabilizes the dopant and makes it more positively charged, which would regulate the adsorption behaviors of gas molecules. Compared with the adsorbed CO molecule, the D-GN4 substrates exhibit high sensitivity toward the O-2 molecule. The individual CO (or O-2) on the Mo-GN4 have the largest energy difference, while they have moderate adsorption energies on B-GN4 sheet. Besides, the dopants (or adsorbed gases) can effectively regulate the electronic structure and magnetic properties of GN4 (or D-GN4) systems, such as the adsorption of O-2 (or CO) can decrease (or increase) the magnetic moment of Mo-GN4 system and the magnetic property of Co-GN4 is enlarged by the adsorbed O-2. As a result, we may distinguish the kinds of adsorbed gases by testing the change in magnetic property of the system, which can provide important reference for exploring the surface reactivity of graphene-based materials and designing the novel gas sensors or spintronic devices. (C) 2017 Elsevier B.V. All rights reserved.