Aiming at the improvement of the band-shaped tube bundle condenser of a 1000MW thermal power unit, this paper uses a porous media model to study the vapor phase flow and heat transfer characteristics of the condenser shell side. The distributions of streamline, velocity, temperature, air mass fraction, and heat transfer coefficient were conducted and analyzed. The back pressure of the condenser with improved band-shaped tube bundle is 5.03 kPa, which is higher than the HEI standard by 0.30 kPa. Analysis shows that the condenser air cooling zone has a better cooling effect, but there are more local vortices at the top and middle of the tube bundle module, which leads to chaos in the flow field and a decrease in heat transfer coefficient. The auxiliary steam inlet channels at the top and middle can be optimized by reducing the flow velocity in the free flow zone, thereby improving the flow field of the condenser and increasing the heat transfer coefficient. The increase of the inlet vapor velocity can enhance the heat transfer of the condenser, but also increase the inhomogeneity of heat transfer coefficient. Therefore, there is still room for optimization of the 1000MW improvement of the peripheral strip tube bundle layout. This study provides a theoretical basis for the optimization design for the condenser.