The invention relates to a reclaimed water treatment method, and particularly relates to a method for deeply treating reclaimed water for supplementary water of circulating cooling water for heat-engine plants. The method comprises the following steps: aerating reclaimed water: firstly adding slaked lime, adding coagulant polymeric ferric sulfate, and adding high-efficiency coagulant aid, precipitating, and extracting upper clear liquid; sterilizing with sterilizing agent, adding sulfuric acid to regulate pH to 7.5-8.0; and adding composite scale and corrosion inhibitor. By virtue of the deep treatment method, the related technical problems of deep treatment, sterilization, scale removing, corrosion resistance, ammonia-nitrogen treatment and the like of reclaimed water in power plants can be solved, technical support is provided to safety and economic application of reclaimed water in power plants, the reclaimed water is recycled as supplementary water of circulating water in power plants, and has remarkably economical, social and environment benefits.