Applying the B3LYP calculations, the reactivity and sensitivity of a graphyne-like BN sheet (BN-yne) were explored toward NO2 gas. The NO2 molecule preferentially adsorbs via its both oxygen atoms simultaneously on two B atoms of both –BN– linkage and hexagonal ring with adsorption energy of −12.5) kcal/mol. The NO2 gas increases the electrical conductance of BN-yne sheet by stabilizing the LUMO level. The electrical conductance of NO2/BN-yne complex is predicted to be much higher than that of the pristine BN-yne nanosheet. We showed that the NO2 gas interacts faster and stronger than the SO2, NH3, CO2, O2, H2O, and N2 gases with the BN-yne sheet, quickly occupying the adsorption sites. Therefore, we conclude that the BN-yne sheet may be promising selective sensor for NO2 gas in the presence of these gases. The recovery time for NO2 desorption from the surface of BN-yne is predicted to be 0.14 ms at room temperature, indicating a short time.