The invention relates to an optimal operation method of circulating water in a power plant. A data acquisition layer, an IaaS layer, a PaaS layer and a process APP layer are included. The method is characterized in that the industrial APP layer comprises automatic identification of production conditions, circulating pump operation mode optimization, mechanical tower fan operation mode optimizationand online calculation of optimization benefit. The optimized operation method comprises the following steps that firstly, data are collected by the data acquisition layer, and an operation sample database is established; secondly, filtering, collating, and storing are conducted at the IaaS layer; thirdly, in the Paas layer, analysis and calculation is conducted by an algorithms library, and a business analysis model is established based on output results; fourthly, automatic identification of the production conditions is conducted in the industrial APP layer, according to the production conditions, online optimization of operation mode of a circulating water system circulating pump and a strong ventilating tower fan is conducted in an operation sample library, and optimization results are output; and fifthly, online calculation of optimal benefits is conducted. Energy consumption of circulating pump operation is reduced, the generating cost is reduced, and economic benefits are improved.