The reuse of reclaimed water as a source of circulating cooling water for thermal power plants is an increasingly common way to save water. However, it has led to troubles such as microbial growth, corrosion and scaling. Herein, the performance of composite agents in scaling inhibition, bactericidal and corrosion inhibition was assessed for commercial Q235 carbon steel in reclaimed water was assessed used as circulating cooling water of thermal power plant via static scale inhibition method, biocide energy efficiency evaluation method, electrochemical and response surface analysis method etc. The test specimens were analyzed in terms of morphology and composition by using SEM, metallography and EDS. The results showed that the optimal formulation of composite chemical agents for the candidate reclaimed water as the recycling circulating cooling water is as follows: scale inhibitor 17 mg/L + biocide 40 mg/L + sodium gluconate 90 mg/L + zinc sulfate 11 mg/L, which presents a scale inhibition rate of 95.7%, a bactericidal effective time of 15 d, and a corrosion inhibition rate of 91.27%. Furthermore, there is a better synergistic effect between the various agents, and the composite agents can inhibit the cathodic and anodic reactions simultaneously. The composite agents can inhibit cathodic and anodic reaction at the same time, which is a kind of hybrid, multi-functional, environmentally friendly agent for cooling circulating water treatment.