A thermal power plant is a power station in which heat energy is converted to electric power. This complex system necessitates a methodology of analysis, modeling and supervision. The objective of this paper is to present initially the architecture of SCADA systems (Supervisory Control and Data Acquisition) in thermal power plants. Then, we present two structured analysis methods: SADT (Structured Analysis and Design Technique) and SA-RT (Structured Analysis for Real Time). Next, we present the diverse steps and tools of a general model for analysis and supervision of control - command systems. Finally, these functional analysis techniques are discussed.