Abstract: Nusselt model is the theory model for predicting the film condensation of a quiescent vapor along an isothermal vertical plate. When the steam condenses inside a vertical, the interfacial shear stress due to the steam flow tends to accelerate the liquid film and to make it thinner which would induce the prediction by Nusselt theory deviating from the measured heat transfer coefficient. Considering the effect of interfacial shear stress, the Nusselt model for film condensation was modified in this paper. By using the Nusselt model as well as the modified model, the heat transfer characteristics of complete condensation in a vertical tube passive condenser were studied. The results show that the interfacial shear stress can change the flow state of vapor and liquid film inside tube and its influence on condensation can not be neglected. The modified model considers the interfacial shear stress appropriately, so the calculated values agree well with the experimental results.