The invention relates to the field of chemical industry cleaning, and discloses a composition for circulating water treatment. The composition contains a heterocyclic compound and hydrophilic colloid with a weight ratio of 1 to (2.5-40), and the heterocyclic compound comprises a first heterocyclic compound of which hetero atoms are sulfur and a second heterocyclic compound of which hetero atoms are nitrogen. The composition preferably also contains a phosphorus-free polymer. The invention also discloses a treatment method of circulating water, and the treatment method comprises the following stages: in an initial stage, adding the heterocyclic compound of 3-12mg/L and the hydrophilic colloid of 30-120mg/L, and performing normal-temperature per-filming; in a concentration stage, adding the phosphorus-free polymer of 6-30mg/L, starting a thermal load and supplementing water; and in a stabilization stage, continuously supplementing water and discharging sewage, and adding an agent to enable the concentration of the heterocyclic compound in the circulating water to be 1-4mg/L, the concentration of the hydrophilic colloid to be 10-40mg/L, and the concentration of the phosphorus-free polymer to be 2-10mg/L. Moreover, the invention also discloses an application of the composition serving a pre-filming agent or a corrosion and scale inhibitor in circulating water treatment. The composition disclosed by the invention does not contain phosphorus, and can effectively achieve pre-filming and corrosion and scale inhibition.