An analytical study is conducted of condensation heat transfer characteristics under reflux-cooling modes with both constant temperature and constant heat flux (CHF) at the inner wall of a single vertical tube. The effects of interfacial shear stress and convection on the reflux condensation hear transfer are examined analytically. The results indicate that interfacial shear retards the condensate flow and thickens the liquid film layer; which in turn decreases the condensation heat transfer coefficient (HTC). The dimensionless film thickness and local HTC with zero convection varies with an increase in the interfacial shear and has a remarkable effect on the condensation process, especially with a larger condensation length. However the film Reynolds number has the opposite effect. Additionally, the interfacial shear thickens the film and retards the liquid flow relatively more distinctly for the CHF case. Finally compared with the experimental data from previous study, the observed trend of the condensation heat transfer can be reasonably described by the present model at moderate film Reynolds numbers.