During certain accidents in a nuclear power plant, a large amount of high-pressure and high-temperature steam will be released into the containment. In some third-generation nuclear power plants, the Passive Containment Heat Removal System (PCS) is employed to protect the integrity of the containment by condensing steam under accident conditions. However, the presence of non-condensable gases such as air in the containment increases thermal resistance in the heat transfer process. In this study, a novel heat transfer enhancement method, involving the installation of guide sleeves outside heat transfer tubes, was proposed. Computational Fluid Dynamics (CFD) method was employed to investigate the heat transfer characteristics of steam–air condensation outside the heat transfer tube within the sleeve. The analysis focused on the condensation heat transfer coefficient under conditions of 0.32 MPa pressure, 0.56 air mass fraction, and 8.67 °C wall subcooling. The influence of the guide sleeve on the heat transfer of the single tube and tube bundle, as well as the influence of the sleeve size, were investigated.The results indicate that guide sleeves significantly impact the condensation heat transfer characteristics of steam. Appropriately designed guide sleeves can enhance flow velocity around the heat transfer tubes, improve the scouring effect on the tube bundle, and disturb the high-concentration air layer on the tube external surfaces, thereby improving heat transfer. The average condensation heat transfer coefficient of the tube bundle can be increased by up to 48.83% at most.