Abstract: A linear analog fault diagnosis approach by means of fault dictionary. is presented to overcome the three major defects in classic fault dictionaries. First, a fault dictionary using node-voltage-deviation-ratio vectors as fault signatures is constructed. The dictionary can detect both the hard and soft faults for each single faulty component in linear circuits, and has some significant features such as less simulation runs, minimal storage space and wide diagnosis scope. Second, how to extend some points of view in geometry to analog fault diagnosis area is discussed, and three geometric models based on the node-voltage-deviation-ratio vectors are designed for faults isolation in case of considering tolerances. Last, two examples are given to verify the methodology. The promising experimental results manifest the correctness and effectiveness of the approach proposed in this paper.