Abstract: An experimental study for fluid hydrodynamic characteristics in thin water films falling down the outside of a vertical tube was performed with the analysis of several factors about the uniformity and stability of the film. Experimental data suggested that there is an optimum value of the annular distance in the range 0.5—2.0 mm and of the spray density in the range 250—700 kg/(m•h) for the falling-film device. Single-tube rotated 270°along the tube wall was used in the falling-film device in order to make the liquid flow tangentially. Several suggestions for the device design of outside tube falling film were proposed.