Abstract: In this paper, there is discussed a fault diagnosis technique and related method of calculation to determine the position and value of a fault component which happens to be in a b-branches network. This technique based on comparing the fault circuit with the adjoint circuit (which is named to indicate the original circuit in normal state) requires only a few measurements on some of accessible nodes or branches.Three main concepts are discussed in this paper: (1) The discussion about the external mapping of the internal faults; (2) The discussion about the extension of a fault state; (3) The discussion about the approach to proventing chain-fault.