Aimed at the problems that in the existing fault propagation models and analysis methods based on qualitative reasoning often neglect the nonstructural failure caused by the drift of performance parameters, this paper proposes a brand new method of fault propagation modeling and analysis, as well as the propagation mechanism, signalaggregation mechanism, influence mechanism, and the reasoning process. In this method, taking the analysis of fault signal strength as a core, the fault signals produced in the source in the connectivity models transmit to each indenture level in the qualitative network model of circuit system through the hierarchical modeling way. Then, the paper adopts the colored qualitative network to evaluate the fault effect and its severity quickly and intuitively. Finally, the paper verifies the practical effect of this method by the autopilot at a certain robot plane.