The horizontal tube falling film evaporator is a liquid distribution device that evenly sprays the feed liquid onto the horizontal tube bundle, forming a liquid film on the outer surface of the tube. Due to gravity, the liquid film flows downward along the outer wall of the tube, and the saturated heating medium inside the tube transfers heat to the medium outside the tube through the tube wall. It has the characteristics of high heat transfer efficiency, small temperature difference loss, short material heating time, low deterioration, low energy consumption, and small equipment volume. Suitable for low viscosity media and insensitive to foaming phenomena that occur during evaporation.