In order to improve the efficiency of automobile fault diagnosis and reduce the cost of diagnosis, this paper proposes a fault diagnosis method of automobile system based on Dynamic Fault Tree (DFT). Firstly, the failure mode model of the system is the DFT is established by using DFT, and the DFT is transformed into a sequential binary decision diagram (SBDD) to calculate the minimum cut set (MCS). Secondly, the diagnostic importance (DIF) of the MCS and the components in the MCS is calculated. On this basis, a diagnosis method for automobile based on the Unified Diagnostic Service (UDS) protocol is proposed. The MCS corresponding to the diagnostic trouble codes are filtered and sorted, and MCS and components with large DIF are prioritized for diagnosis. Finally, the effectiveness of the proposed method was verified by the case study of an Active Rear Steering system. The case analysis results show that, the proposed method can calculate the fault diagnosis sequence and can effectively guide the vehicle fault diagnosis work.