The laminar liquid film falling on a horizontal smooth tube is studied numerically. The instantaneous hydrodynamic characteristics of falling film flow, the importance of surface tension in calculation and the effects of film flow rate, tube diameter, liquid distributor height and inlet liquid temperature on the flow field and film thickness are elucidated. The results indicate that: (1) The surface tension is important in the calculations of falling film flow on a horizontal tube; (2) The film falling on a circular tube has obvious instantaneous behaviors; (3) The film thickness increases with increase of film flow rate, while decreases with increase of the tube diameter, liquid distributor height and liquid temperature, respectively; (4) The film distribution along the peripheral angle is unsymmetrical, and the minimum thickness appears in 110-150 of peripheral angle depending on the working conditions. Furthermore, new correlations of falling film thickness on a horizontal tube based on the present data are established, which fit 97% of 84 data in theta = 2-15 degrees within 20%, 90% of 632 data in theta = 15-165 degrees within 20%, and 73% of 112 data in theta = 165-178 within +/- 30%. (C) 2017 Elsevier Ltd. All rights reserved.