The invention discloses a modifying agent for preventing calcium halide scaling. The modifying agent is prepared from, by mass, 15-25 parts of amino trimethylene phosphonic acid, 4-8 parts of docusate sodium, 2-3 parts of cetyltrimethylammonium chloride, 0.1-0.3 part of tributyl phosphate and the balance water. The modifying agent has the advantages of being high in scaling resistance, small in use amount, easy to construct, not capable of increasing operation workloads, high in flow-back capacity, capable of saving cost, and the like.