The utility model provides an underpressure distillation device, includes the underpressure distillation tata body, the gaseous export of top of the tower, vacuum system, subtracts a line extraction mouth at the tower tray, subtracts a ray of draw -off pump, subtracts a ray of first heat exchanger, subtracts a ray of second heat exchanger, subtracts two line extraction mouths, subtracts the second line draw -off pump, its characterized in that: the top of the tower is gaseous to be exported and the vacuum system intercommunication, subtracts a line extraction mouth and subtract a ray of draw -off pump entry to feed through, subtracts a ray of draw -off pump and exports and subtract a ray of first heat exchanger and subtract a ray of product pipeline intercommunication, subtracts a ray of second heat exchanger and subtracts line backward flow mouthful intercommunication, and the reducible steam quantity of the device, reduction energy consumption, reduction sewage discharge reduce decompression top of the tower section equipment casing size.