The invention discloses a method for treating papermaking wastewater into clear water to discharge. According to the method, a grating, primary sedimentation tanks, an efficient shallow air flotationdevice, hydrolytic acidification tanks, contact oxidation tanks, secondary sedimentation tanks and qualified water tanks are used. By the method, few equipment is used, the cost is low, the operationis simple and convenient, the treatment effect is good, and detection proves that after treatment, the CODcr removing rate is 96%, the SS removing rate is 95%, the ph value of the treated effluent water is 6.0-9.0, the CODcr content is smaller than or equal to 100mg/L, and the SS content is smaller than or equal to 70mg/L. According to the method, wastewater treatment comprises the following aspects: a whole technology, equipment, an additive, labor and the like; the wastewater treatment cost is 0.40 Yuan/m3; at present, only 10 tons of water is needed for making one ton of paper, but in the original conventional papermaking technology, 30 tons of water is consumed for making one ton of paper, and the difference between the two indexes is a reasonable expense; after extraction of lignin from high-Ian wastewater, a black liquor can become a useful resource, the lignin is prepared, produced mid-stage effluent water and paper-making white water are treated by the method into the clear water, and the clear water is discharged, so that the wastewater causes zero pollution to natural water.