The invention relates to an oil field flooding stratum protective agent and a preparation method and application of the oil field flooding stratum protective agent. The oil field flooding stratum protective agent comprises the following components: 20%-22.5% of polycarboxylic acid, 20%-22.5% of organic phosphoric acid, 3%-5% of nonionic surfactant, and the balance being water. The polycarboxylic acid is selected from polyacrylic acid or hydrolysis polymaleic acid, the organic phosphoric acid is selected from phosphorus base butane tricarboxylic acid or hydroxyl phosphono acetic acid, the nonionic surfactant is alkylphenol polyoxyethylene ether, and the percentage is weight percentage. The oil field flooding stratum protective agent and the preparation method and the application of the oil field flooding stratum protective agent have good application prospect for economic and effective development of a clastic rock oil reservoir, and especially a low permeability reservoir.

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