To develop total energy systems and reveal characteristics of polygeneration systems, we have investigated one coal-based polygeneration system for power and methanol production, and compared it with its original individual processes. The results indicate that the polygeneration system will save 3.9-8.2% energy compared to the individual processes. By the aid of graphical exergy analysis and comparison of systems, we have indicated some specific information on internal phenomena. The result reveals that synthesis on the basis of thermal energy cascade utilization is the main contribution to the performance benefit of the polygeneration system. Moreover, the capacity ratio of chemical process to power system strongly affects matching between two sides, which is a key criterion in polygeneration system. Hence, synergetic integration of the power system and the chemical processes in polygeneration systems will provide promising performance in the future. (C) 2004 Elsevier Ltd. All rights reserved.