The invention belongs to the circulating cooling water treatment technical field, and refers in detail to an environment-protecting composite pretreatment filming agent used for the pre-treatment filming in a circulating cooling water system and a use method thereof. The environment-protecting composite pretreatment filming agent comprises the main components of 2-phosphonobutane- 1, 2, 4-tricarboxylic acid and sodium of polyepoxysuecinic acid as well as a proper amount of carboxylic acid copolymer, benzotriazole, sodium molybdate, zinc sulphate and so on. When used, the composite pre-treatment filming agent is added into the circulating cooling water directly, and a corrosion-resistant protecting film is formed after 48 years of operation, the corrosion resistance of which to the standard copper sulphate drip solution is far better than the traditional phosphor-zinc pretreatment filming agent. The total phosphor content of the environment-protecting composite pretreatment filming agent is less than 7.5mg / l, and the water pH value does not have to be adjusted. After the pretreatment filming, the water is clear and transparent, and the normal operation can be started without replacing the water. Thus, not only the water to be replaced is saved, but also the chemical base investment expense during the normal operation after the water replacement is reduced. Meanwhile, no waste liquor of pretreatment filming is discharged, so the invention belongs to the environment-friendly pretreatment filming method.