The degeneration of its thermoelectric properties in air is one of the factors that limit the practical application of high-performance n-type Mg3Sb2. In this work, first-principles calculations are conducted to study the adsorption of O2 and H2O on the Mg3Sb2(10-11) surface, as well as the effect of two strategies based on a terminating atom and Al doping on the adsorption performance. The calculated results show that the adsorbates prefer to adsorb on the bridge site of the surface because of the interaction with the outermost Mg atom. Sb termination can weaken the adsorption actions, due to the decreased interaction between the adsorbates and Mg atoms resulting from the decreased O-Mg bond strength. In addition, Al doping makes O2 prefer to interact with an Al atom rather than a Mg atom, which is beneficial for reducing Mg loss and thus improving the performance stability. This work aims to provide insight into improving the thermoelectric performance stability of Mg3Sb2-based materials.