Abstract: System KBFS is a knowledge-based system.It will turn into an expert system in thefield,if the contents in its KB is replaced with knowledge in some application field.According tostructure of knowledge,knowledge in KB of KBFS is represented by the method of combining decla-rative representation with procedure representation.Meta-level space and object-level space constitutethe knowledge space of KBFS Inference in KBFS is even more correct and effective,because inferencein recta-level guides inference in object-level.