The invention discloses a method for purifying long chain dicarboxylic acid in fermentation broth. The method comprises the following steps: (I) adding inorganic salts and an alkali solution into fermentation broth, and stirring to dissolve the inorganic salts, wherein under the synergistic effect of alkali and salts, the cell wall of bacteria are dissolved, broken, and demulsified; (II) allowing the system to stand still to carry out layering, removing solid impurities such as bacterium dregs, and recovering alkane; (III) adding a proper amount of polyglycol into the fermentation broth, and dissolving the polymer to prepare a dual water phase system; (IV) subjecting the obtained dual water phase system to a super gravity treatment, wherein after the super gravity treatment, the upper phase and the lower phase are rapidly separated, proteins and pigments are dissolved in the upper phase, and the product (dicarboxylate salts) is dissolved in the lower phase; and (V) acidifying the lower phase obtained in the step (IV) to precipitate dicarboxylic acid crystals, and performing cooling, filtering, water washing, and drying to obtain a refined dicarboxylic acid product. A dual water phase extraction technology and a super gravity technology are combined to refine long chain dicarboxylic acid, the technical flow is shortened, the investment of equipment, time, and energy is saved, and the refined product has the advantages of high purity and low content of total nitrogen.