Along with the cogeneration units constantly put into operation, the problems of electric load control and peak-load regulation for heat supply unit during heating period have attracted a wide spread attention, and the online real-time monitoring system is helpful to solve these problems. Taking online real-time monitoring system in Jilin Songhua River Thermal Power Plant as an example, this paper investigated the design and application of this system, such as system composition, software function and so on, put forward the matters needing attention in the design as well.