TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Composite Oil Displacement Agent: The composite oil displacement agent comprises the following main components by parts by weight: 20-40% P. albofiavus (CGMCC 4670) bacterial liquor, 6-30% surfactant, 5-10% polymer modifier, 1-10% viscosity breaking agent, 1-5% additive, and the residual water, where the concentration of the bacterial liquor is 108-1010/g. The bacterial liquor comprises the following according to weight percentage: 20-30% sugar, 1-5% potassium di-hydrogen phosphate (KH2PO4), 1-5% magnesium sulfate (MgSO4), 1-5% ammonium sulfate ((NH4)2SO4), 1-5% corn steep liquor, 20-30% nitrogen source, and the residual water, and the pH is 6-7. The polymer modifier is selected from sorbite, xylose, gelatine, reducing glue, soluble starch, sodium methyl cellulose, methyl cellulose M20, hydroxyethylcellulose, hydroxy propyl cellulose, polyethylene glycol 600, polyethylene glycol 6000, polyvinylpyrrolidone, and poval, or their mixture. The surfactant comprises non-ionic surfactant and amphoteric ion surfactant; the weight percentage of the non-ionic surfactant in the total weight of the oil displacement agent is 3-15%, and the weight percentage of the amphoteric ion surfactant in the total weight of the oil displacement agent is 3-15%. The non-ionic surfactant is selected from isooctyl phenolic polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, nonyl phenol polyoxyethylene ether, polyethylene glycol octyl phenyl ether, oleic acid polyoxyethylene ether, fatty acid polyoxyethylene ether, hexamethylene tetramine and polyoxyethylene alkylamine. The amphoteric ion surfactant is selected from carboxylic acid betaine, N-acylamino carboxylic acids betaine, alkyl thionocarboxylic acids betaine, and cocamidopropyl betaine. The viscosity breaking agent is selected from non-ionic-phosphate salt type, non-ionic-sulfate salt type, non-ionic-carboxylate salt type and non-ionic-sulfonate type, and lauryl amido polyoxyethylene ether phosphate. The additive is selected from isopropanol, n-butyl alcohol, normal propyl alcohol and ethanol.