This expert control system is capable of providing 1) tracking of the errors or faults in the combustion process, 2) diagnosis and analysis of them, and 3) the feedback process control. The combustion process is routinely susceptible to large number of operational problems. Knowledge-base of expert control system is represented through interrelation analysis bewteen control and operation variables obtained from the combustion process modeling. All knowledge in this system was organized into a unique hierarchical structure, and represented using an IF-THEN rule-based formation. Based on the rule-based expert system by on-line mode, the intelligent process operation aid system for the combustion plant was completed to provide an integrity in optimal operation and control.