The numerical investigation was performed to analyze the film thickness characteristics over fully wetted horizontal round tube in a falling film evaporator using commercial CFD code Fluent 6.3.26. A two-dimension multi-phase flow model for numerical simulation was developed under adiabatic condition. The temporal variation characteristics of film flow process and the steady film thickness distribution over horizontal tubes were analyzed in detail. It was found that the whole process of liquid film flowing along the horizontal tube surface includes the transient sub-process and steady state sub-process, and the former can be divided into five stages to be analyzed. The obviously asymmetric distribution of film thickness is captured by the simulation results. The film thickness increases with the increase in film Reynolds number. An obvious zone without liquid is formed very closely to the lower stagnation point, and the size of the zone is bigger when the Reynolds number is higher. (C) 2015 Elsevier Ltd. All rights reserved.