The invention discloses a reduced pressure
distillation method and a reduced pressure
distillation device. A flash
tower is arranged between a reduced pressure furnace and a reduced pressure
distillation tower, an oil
transfer line is canceled, a reduced pressure distillation
raw material is heated in the reduced pressure furnace and then directly enters the flash
tower, and gas-liquid separation is performed in the flash tower; the
liquid phase, namely flash bottom oil, discharged from the bottom of the flash tower is introduced into the reduced pressure distillation tower; and the
gas phase, namely flash top gas, discharged from the top of the flash tower is condensed into
liquid phase, and the
liquid phase is led out of the device. According to the reduced pressure
distillation method and the reduced pressure distillation device using the flash tower in back of the reduced pressure furnace, on the one hand, the yield of reduced pressure distillate is improved; and on the other hand, the conventional reduced pressure oil
transfer line is canceled, the operation load of the reduced pressure tower is reduced, and the
diameter of the reduced pressure tower can be properly reduced so that the equipment investment is saved and the operation cost is lowered.