According to the overall construction objectives and requirements of the first and second phases of a thermal power plant, a three-layer SIS system was designed. The key issues such as network architecture, interface design, software and hardware selection, and function setting were discussed and analyzed, and the functions and implementation methods of subsystems such as report calculation, production process monitoring and data management, performance calculation and economic analysis, unit load optimization distribution, main and auxiliary machine condition monitoring and life calculation were introduced. The actual operation of the power plant shows that the designed SIS scheme is feasible.