Based on micro-nano sensing technology, the structural and electronic characteristics of metal-doped boron nitride monolayer are investigated by first principles. The existing nano sensors have practical problems, such as no selectivity, too strong adsorption capacity to be recycled, too weak adsorption capacity to obtain sufficient response. We explore the use of a highly sensitive recyclable nano sensor that is best suited for sensing function. Gas adsorption properties for the toxic decomposition gases of C4F7 N are further developed. We select the N-vacancy with the highest binding energies, which are −6.34 eV when doped by Co atom. The strong interaction and suitable adsorption energy between the activated atoms of adsorbent and gases prove their unique adsorption properties. Since no new chemical bonds are formed, it is obvious that systems are in the form of physical adsorption, which proves their ideal desorption properties. In addition, the conductivity increases to different degrees due to the redistribution of electrons, which proves excellent selectivity. Hence, we propose the use of Co-BNN nanomaterial for the detection of C4F7N toxic decomposition gases. Results would serve as instructive reference for the investigation of resistive gas-sensitive sensors.