Disclosed is a heptane sulfonate of a targeted drug conjugate modified by a multi-arm, water-soluble polymer. The typical heptane sulfonate of the conjugate comprises one to eight molecules of heptane sulfonate. Preferably, each branch respectively binds to a conjugate with two molecules of heptane sulfonate, and the preferred heptane sulfonate of the conjugate is eight molecules of heptane sulfonate. The present invention is a targeted anti-cancer conjugate modified by the multi-arm polymer, wherein modification by the water-soluble polymer can enhance the water solubility of the conjugate and increase a drug loading amount; and a targeting molecule enhances the targeting property, allowing the conjugate to be at a higher concentration in a target tissue.