Abstract: In this paper, it is proved that the direction of the node-voltage difference vector, which is the difference between the node-voltage vector at faulty state and the one at the nominal state, is determined only by the location of the faulty element in linear analog circuits. It is further proved that the direction of the sensitivity vector indicates the location of the faulty element. Considering that the module of the sensitivity vector is the weight of the faulty element's parameter deviation to the voltage deviation, fault dictionary is set up based on node-voltage sensitivity vectors. A decision algorithm is proposed in consideration of both the location and the parameter deviation of the faulty element. Single soft fault with tolerance in analog circuit can then be diagnosed. The validity of the theory and the availability of the method are verified by simulation results.