The invention discloses a four-tower distillation and membrane separation integrated system, which comprises a mash liquid pre-heater, a negative pressure mash tower, a normal pressure mash tower, a medium pressure rectification tower and a high pressure rectification tower, wherein the high pressure rectification tower is sequentially connected to an alcohol gas overheating device and a membraneseparation device through pipelines, the membrane separation device comprises a low vacuum membrane assembly and a high vacuum membrane assembly, and the low vacuum membrane assembly and the high vacuum membrane assembly are connected in series. The method for distilling ethanol by using the system comprises that A, gas is removed from fermented mature mash to form degassed mash; B, the alcohol vapor is separated from the waste mash liquid in the degassed mash; C, the alcohol vapor is condensed to form a crude alcohol, the crude alcohol is distilled by the medium pressure rectification tower,and the obtained material enters the high pressure rectification tower; and D, the alcohol vapor entering the high pressure rectification tower is partially overheated, and the obtained material sequentially enters the low vacuum membrane assembly and the high vacuum membrane assembly to separate the ethanol and the water. According to the present invention, with the system and the method, the phenomenon of alcohol volatilization in the distillation process can be avoided, the consumption of freezing water and steam can be reduced, and the system and the method are energy-saving and environmentally friendly.