The invention discloses a ferroresonance fault knowledge base construction method, and the method is used for constructing a ferroresonance fault knowledge base including faults caused by lightning stroke, three-phase breaker different-term switching-closing, broken line fault, singlephase earth fault, and arc light earth fault; the ferroresonance fault knowledge base construction method comprises a knowledge base updating module, a knowledge base, an integration database module and a control module; the knowledge base updating module comprises an automatic knowledge obtain module and an interaction knowledge obtain module; the knowledge base uses a generative system expression method; the integration database module stores knowledge base rule basic elements; the control module can control open/close of the automatic update database module according to comparison between the data in the present integration database and rules in the knowledge base, and the control is also based on expert inquiry. The method can construct the ferroresonance fault knowledge base system so as to provide helps for auxiliary decisions of fault maintenance personnel, and the knowledge base update module can improve knowledge base system completeness and accuracy.