The steering by wire (SBW) system of electric vehicle results in the decrease of steering reliability. The structure of SBW system and the normal operation and failure mode of components were described by using the method of automatic fault tree construction, and the standard parts library was established. The standard fault tree was built by drag-and-drop method. After the automatic construction of the fault tree, the reliability of SBW system was analyzed quantitatively based on the fault tree. The results show that the fault tree method can quickly find the weak links of the system and improve the reliability of the SBW system on the basis of the system optimization design.