Abstract: The paper presents a diagnosis method based on fault tree model andrealizes a diagnostic system. First, a hierarchical diagnosis model is presented and acertain reasoning strategy and a possible reasoning strateyg are proposed. Secondly, afault tree-objected and frame and generalized rule based hybrid knowledge representation method is presented. Finally, the diagnostic system is realized in BORLANDC+ +, using COMPAQ 486 with WINDOWS operating platform, and demonstrated bydiagnosing a circuit testbed.