Abstract: By establishing physical and mathematic model for R113 falling film evaporation in vertical tube of an annular membrane evaporator, two-dimensional unsteady numerical simulation was conducted on heat transfer characteristics of the gas-liquid countercurrent falling film evaporation, so as to analyze the distribution of liquid film flow, wall temperature and film surface temperature, and to compare the thickness of liquid film before and after heating. Results show that in the process of falling film evaporation, the splash of droplets starts from the lower end of liquid film, which propagates gradually toward the upper end; for R113, both the wall and film temperature rise along the flow direction during falling film evaporation, while the gas temperature falls; the temperature reduces gradually from wall to center along the radial direction, and the temperature distribution tends to be opposite at the position 1 mm away from the wall; the thickness of liquid film reduces greatly after heating, when the thickness of downstream film becomes relatively uniform.