The analysis of the composition of chemical oxygen demand (COD) can provide a theoretical basis for the design of an efficient wastewater treatment process. In this study, the gradient membrane molecular weight division method was selected to create the COD fingerprint of the oil production wastewater. The chemical components and concentrations of the organic pollutants in the wastewater were analysed by gas chromatography-mass spectrometry, and the structures were qualitatively analysed by UV-Vis. Results showed that the types of aromatic hydrocarbons decreased from 163 to 96 in the advanced wastewater treatment, the types of straight-chain hydrocarbon organics were increased from 17 to 25, which changed from C14–C30 to C14–C38. By contrast, the total concentration of COD was decreased by 80.5% (from 237.5 mg/L to 46.3 mg/L). The organic pollutants in the wastewater were mainly aromatic hydrocarbons and straight-chain alkanes. The results also indicated that the removal of the petroleum macromolecules and soluble organics will be necessary for the treatment of the polymercontaining oil production wastewater.