As a high level application module of SIS system, the on-line monitor and analysis system for energy-saving is widely applied to power plants. But the corresponding guide system which applied effectual guidance to realize optimal operation is still lack of sufficient research. The main purpose of the guide system is to confirm the certain reason which leads to energy loss among various reasons. Then the effective operating adjustment or timely maintenance could be implemented to reduce losses. As the symptoms, the operating parameters always depart from their target values. And the symptoms have determinated logical relations with certain reason which leads to energy loss. With detail description of the function and structure of the guide system, the concepts of operating target value and parameterspsila offset degree are put forward in this paper for the first time. And the curves of some important parameterspsila operating target values are obtained by off-design condition analytic method with analysis of historical data. Furthermore, the logical matrixes which quantitatively describe the logical relations between symptoms and reasons are established by the method of symbolic logic. The research of the paper provides the important theory foundation to the exploitation of the guide system for energy-saving in power plant.