Abstract: The secondary sedimentation tank effluent of a corn deep-processing wastewater treatment plant (WWTP) by EGSB+A/O process was classified by ultrafiltration membrane separation. The molecular weight distribution characteristics of effluent dissolved organic matter were investigated by measuring DOC, UV₂₅₄ and three-dimensional fluorescence spectrum. The results showed that the dissolved organic matter (DOM) of corn deep-processing WWTP secondary effluent was mainly substances with molecular weight greater than 10 k and less than 0.5 k, the aromatic structure was rich in these two molecular weight components. Three-dimensional fluorescence spectroscopy showed that the effluent mainly contained tryptophan protein-like and humus substances, the fluorescence intensity of humus of each molecular weight range was greater than that of proteins, and humus was generated in aerobic aeration stage. The total fluorescence intensity of organic matter of each molecular weight range showed a significant linear correlation with DOC and UV₂₅₄.