By means of density functional theory (DFT), the most stable structures of NH3 and NO2 molecules adsorbed by different layers of GeSe were studied. The adsorption properties of the adsorption system were studied from the aspects of adsorption energy, band gap, state density, differential charge density and recovery time. Significant adsorption energy (−1.060 eV, −1279 eV, −1.390 eV), charge transfer (−0.370e, −0.382e, −0.379e) and electron localization function (ELF) indicated that NO2 was chemisorbed on the surface of GeSe. The recovery time indicates that the mono-layer GeSe adsorption NO2 system can complete the desorption between 298 K and 398 K, and the bi-layer GeSe adsorption NO2 system can complete the desorption in a shorter time with the recovery time of 8.66S at the temperature of 498 K. Therefore, the theoretical research in this paper provides a theoretical basis for the development of GeSe gas sensors for the detection of harmful gases NH3 and NO2.