Rectifying tower is mainly designed to ultimately guarantee alcohol content, fusel oil and impurity content in the alcohol products. A number of fusel oil outlets are mounted on siding in the lower middle part of the tower, and a number of alcohol discharge outlets are arranged on the top of the tower, so as to adjust the alcohol content and quality. Alcohol will be conveyed from rectifying tower to methanol tower for further distillation. Fusel oil from the middle of the tower will be discharged to the recovery tower after weak liquor is separated. Wastewater of the rectifying tower is discharged from the bottom of the tower. Secondary steam from wastewater enters the impurity tower through flashing as a part of heat source of the rectifying tower. Heating of the rectifying tower is realized by saturated steam, and the rectifying tower works at positive pressure.