Belonging to the field of polymer stabilizers, the invention particularly relates to a stabilizer for a polymer solution under high-temperature and high-salt conditions, a preparation method and application thereof. The stabilizer of the polymer solution under high-temperature and high-salt conditions comprises the following components by mass: 10-20 parts of lignin, 5-10 parts of hydrogen peroxide, 5-10 parts of sodium carbonate and 900-1000 parts of deionized water. Hydrogen peroxide in the stabilizer for a polymer solution under high-temperature and high-salt conditions can properly oxidizelignin to remove divalent metal ions contained in the lignin, the treated lignin can effectively remove oxygen and free divalent iron ions from prepared water, so that thiourea can be replaced, the stability of the polymer solution is better improved, the cost can be lowered, and the environment can be protected.