Abstract: This paper numerically investigated the tube bundle effect on steam condensation in the presence of air. Simulations were firstly performed based on the 3 by 3 tube bundles with various tube pitches. Via these cases, the tube bundle effect was defined and the effects of tube pitch on local and average condensation heat transfer were discussed. Then at a tube pitch of 1.5d, the effect of bundle structure on the condensation heat transfer was evaluated. Results indicate that the bundle effect includes the high concentration air layer inhibition effect and the bundle suction enhancement effect. With the decreasing of the tube pitch, the second and third type tubes are mainly influenced by the high concentration air layer effect, and the first type tubes mainly by bundle suction effect. At 1.5d tube pitch, the average heat transfer coefficient for the second and third type tubes decreased 6% and 29% compared to the single tube. In comparison, the first type tubes increased 2.5%. At the tube pitch of 1.5d, the bundle suction effect increases with the increasing of the tube column, resulting in an enhancement of bundle average condensation heat transfer coefficient. For the 3 by 20 bundle structure, the bundle average heat transfer coefficient exceeded that of the single tube.