The invention provides a two-stage falling-climbing film evaporator. An evaporation chamber I and an evaporation chamber II are connected at the lower end by a communication pipe; the middle part of the communication pipe is disconnected; the disconnected part of the communication pipe is provided with a screw; the screw is fixed with an outer screw connection ring; the lower end of the evaporation chamber II is communicated with a separation chamber through a liquid drain pipe; the lower end of the separation chamber is provided with a finished-liquid outlet pipe; the upper side surface of the separation chamber is provided with a secondary-steam outlet pipe; a plurality of climbing-film heat-exchanging pipes and a plurality of falling-film heat-exchanging pipes are respectively arranged in the evaporation chamber I and the evaporation chamber II; the upper ends and the lower ends of the climbing-film heat-exchanging pipes and the fall-film heat-exchanging pipes are respectively fixed in a sealing ring and extend to the side opposite to the sealing ring. The bottom of each of the evaporation chamber I and the evaporation chamber II is divided into two chambers by the climbing-film heat-exchanging pipes and the falling-film heat-exchanging pipes. With the adoption of the evaporator, the raw materials are subjected to the two-stage evaporation, therefore, the evaporating efficiency is higher; and meanwhile, the apparatus is small in size, so that the occupied space in plants are saved.