Horizontal tube falling film evaporator core part -- liquid distributor with distribution at the bottom of the tube and a liquid distributing pipe connecting structure form, compared with the widespread use of domestic vertical tube falling film evaporator, which greatly improves the efficiency of heat exchange. Horizontal tube falling film evaporator with different tube existing falling film evaporator, which is evaporating solution in the heat exchange tube surface film like distribution, and in the steam heating tube, the heat transfer coefficient is two times of the vertical tube type falling film evaporator. Tube falling film evaporator in addition to falling film evaporator heat transfer coefficient is higher, suitable for heat sensitive materials, temperature difference of heat transfer loss is small, easy to realize multi effect evaporation, the liquid film in the heat exchange tube, also has the film structure, easy observation etc..