The invention discloses a composite plugging agent, which belongs to the field of water plugging of oil well. The composite plugging agent comprises the following components by weight percentage: 0.18-0.30% of hydrolysis polyacrylamide, 4.0-6.30% of a biopolymer used for oil extraction, 0.2-1% of a resin cross-linking agent, 0.14-0.5% of a crosslinking promotion agent, and the balance of water. A preparation method of the biopolymer used for oil extraction comprises the following steps: a) preparing a medium, disinfecting the medium at 100-130 DEG C and 0.08-0.12 MPa for 20-40 min, wherein the medium comprises the following components by weight percentage: 4-6% of cane sugar, 0.3-0.5% of sodium nitrate, 0.02-0.04% of magnesium sulfate, and 0.40-0.60% of disodium hydrogen phosphate. and b) using the medium for bacterial strain enlargement culture on pseudomonas, performing two-stage fermentation, and when the viscosity of a broth is greater than 100 mPa.s and the shearing value is more than or equal to 4, obtaining the biopolymer used for oil extraction. The composite plugging agent has the advantages of a simple formula, is suitable for medium and low temperature stratum, also has excellent water plugging performance for high temperature stratum at the temperature of 90-120 DEG C, and is convenient for large-scale popularization and application.