This work using the density functional theory simulates the strong potential of the CuO-decorated PtSe2 (CuO–PtSe2) monolayer as a recycle use C2H2 and C2H4 sensor in order to realize the arc discharge monitoring based on the nano-sensing method. Results indicate that CuO decoration causes strong n-type doping for the PtSe2 monolayer with a binding force (E b) of −2.49 eV, and the CuO–PtSe2 monolayer exhibits strong chemisorption and electron-accepting properties in the two gas systems, with the adsorption energy (E ad) and charge transfer (Q T) obtained as −1.19 eV and 0.040 e for the C2H2 system and as −1.24 eV and 0.011 e for the C2H4 system, respectively. The density of states reveals the deformed electronic property of the CuO–PtSe2 monolayer in gas adsorptions, and its sensing mechanism based on the change of electrical conductivity and the work function are uncovered. This work sheds light on the metal-oxide-decorated transition-metal dichalcogenides for gas sensor applications and would provide the guidance to explore novel sensing materials in many other fields as well.