The present invention relates to a long-chain mixed dicarboxylic acid extraction method, which comprises: (1) adding a mixed dicarboxylic acid solid to water, heating, adding an alkali to adjust the pH value, dissolving, cooling, precipitating, and separating to obtain a solid I; (2) pouring the solid I to water, heating to increase the temperature, and after dissolving the solid I, adding an oxidizing agent to oxidize so as to improve the solution color and reduce the high carbon number dicarboxylic acid content in the solution; and (3) adding an acid to the obtained solution to adjust the pH value so as to precipitate the mixed dicarboxylic acid, separating the solid, and drying to obtain the long-chain mixed dicarboxylic acid finished product. According to the present invention, the second precipitation and the oxidizing process are combined in the water phase to obtain the high quality dicarboxylic acid finished product, wherein the dicarboxylic acid finished product has characteristics of white color, good quality, and low high-carbon-number dicarboxylic acid (dicarboxylic acid having more than or equal to 16 carbon number) content, and is especially suitable for the anti-rust field; and with the extraction process, the by-product discharge problem during the long-chain dicarboxylic acid production can be simply and effectively solved, such that the environment is protected and the enterprise incomes are increased.