The interference mechanism of H2S impurity on the CO2 adsorption performance of solid amine adsorbents is still lack of comprehensive research. An aluminum-based solid amine adsorbent (PEI@Al2O3) was prepared with Al2O3 as a support to load polyethyleneimine (PEI), and the influence of H2S on the CO2 adsorption capacity, adsorption rate and cyclic adsorption performance of the adsorbent was investigated. The results show that the competitive adsorption occurs when H2S and CO2 coexist due to H2S and CO2 simultaneously grabbed the active sites of amine groups on the adsorbent. However, the adsorption competitiveness of CO2 is larger than that of H2S under the simulated biogas condition (i.e., 40% CO2+59.5% CH4+0.5% H2S), thus inhibiting H2S adsorption. Furthermore, the optimal adsorption temperature of CO2 and H2S is inconsistent, and the CO2 adsorption capacity and cyclic stability of PEI@Al2O3 are not disturbed by H2S at the optimal adsorption temperature of CO2.