The invention discloses a high molecular antistatic agent and a preparation method thereof. The high molecular antistatic agent is a copolymer which is formed by polymerizing a benzene ring monomer and a polymer, wherein the benzene ring monomer contains sulfo and carboxyl, and the polymer contains a polyether block and a polyamide block; the end groups of the polyether block and the polyamide block are carboxyl; the monomer and the polymer are synthesized into the high molecular polymer under the vacuum condition. The high molecular antistatic agent has the advantages that the durability, heat-resistant property, compatibility and antistatic property are excellent; the high molecular antistatic agent is mainly applied by being added into matrix resin, and is an internal millable type antistatic agent.