The invention discloses a gradient sub-boiling distiller and a distillation method. The gradient sub-boiling distiller comprises a condensation tube, an evaporation surface, a heater, a liquid distributor, a tail liquid tank, a condensate liquid tank, a tail liquid tube, a liquid inlet tube, a condensate liquid tube and a shell, a raw material liquid is preheated by the condensation tube, is further heated in the heater, flows down from the evaporating surface, and continuously evaporates, the temperature continuously decreases, obtained steam condenses on the surface of the condensation tube,condensing heat preheats the raw material liquid in the condensation tube, and the flowing direction of the raw material liquid in the condensation tube is opposite to the flowing direction on the evaporation surface. The gradient sub-boiling distiller and the distiller have the advantages of completeness in recovery of the condensation heat, increase of the energy efficiency, water cooling waterreduction, water resource saving and energy consumption reduction.