After analyzing the information transfer characteristics of large-scale complex systems,a new fault description model-fuzzy probability signed directed graph(FPSDG) was proposed by introducing the status association probability,fuzzy information and object-oriented technology in SDG.

Signed Directed Graph (SDG) is used for a mathematical model representing the influences among elements of the system, which considers the characteristic of system’s structure and can deal with the complex process of system in a large-scale, and it is a self-contained method to diagnosis system failures.

There are two topics about the method being given: fault propagation digraph and signed directed graph( SDG) .

Recently,the marked development of qualitative simulation research based on the signed directed graph (SDG) has led to SDG be the most effective method in fault diagnosis.

Aiming at the difficulty of quantitatively description of the problem that the information is ambiguous,incomplete,comparatively illegibility in the process of material supply simulation,a sign-directed graph(SDG) method of qualitative simulation is introduced to analyze the material purvey process in qualitative way.

The deviation of SDG node is fuzzed as qualitative fuzzy deviation,and the new deviations of child nodes are fused into the possibility of fault source of parent node with the analysis of the character of fault information transfer and the adventage of dealing with different malfunction cases.