Shale gas as an unconventional resource is an important energy to alleviate the energy crisis and develop low-carbon energy. In CCUS CO2 injected into shale gas reservoirs usually comes from CO2-rich industrial waste gas (IWG), which includes a variety of impurities, such as H2S. Moreover, the CO2 separation from the CO2-rich IWG is a high cost. Therefore, CO2/H2S co-injection is the focus of research. The effect of CO2-rich IWG (with H2S) injection into a shale reservoir is different from pure CO2. We used grand canonical Monte Carlo (GCMC) simulation to examine the competitive adsorption behavior in kerogen slit nanopores for CH4/CO2/H2S mixture. To study the impact of the CO2/H2S co-injection on CO2 sequestration and shale gas recovery. We carefully compare the difference between CO2 and CO2/H2S mixture to shale gas recovery and between CO2/H2S and CO2 sequestration in kerogen slit nanopores. We found the CH4 adsorption capacity is the weakest compared to CO2 and H2S. For CH4/CO2/H2S mixture competitive adsorption, CO2 and H2S occupy more adsorption points, leading to competitive adsorption beneficial to CH4 recovery. The CO2/H2S co-injection can enhance well shale gas recovery like CO2 injection, total recovery is about 70%. And in low pore size the effect of recovery is more obvious by co-injecting CO2/H2S. This work provides important insights into CO2/H2S co-inject into shale kerogen reservoirs, thus helping to reduce CO2 injection expense.