First-principles calculations are performed to study the structure, stability, density of states and work function of toxic gases (NH3, SO2 and NO2) molecules adsorption on GeSe monolayer with point defect engineering, including Ge/Se mono-vacancy, anti-site defect, and P atom substituted defect. Our results on the adsorption energy, charge transfer and electron localization function show that the interaction between gas molecules and point defects in GeSe monolayer is sensitive, which causes significant modification to the electronic structure and work functions of GeSe monolayer. (C) 2018 Elsevier B.V. All rights reserved.