Abstract: Flexible DC transmission has advantages of flexible power conversion and high transmission capacity. Fast and sensitive fault detection technology is extremely important for the safe and stable operation of DC network. The presence of transition resistors, the configuration of current limiting reactors and the influence of measurement noise facilitate the transient characteristics after faults to be weak, which restricts the application of most fault detection methods. To this end, this paper proposes a short-circuit fault identification method for DC transmission systems based on virtual power ratio. Firstly, the fault characteristics of the multi-terminal DC transmission system are analyzed, and the equivalent circuit after failure is simplified by using virtual neutral point to clarify the differences between faults inside and outside the zone. On this basis, a virtual power ratio is proposed to enhance the characteristic differences after fault occurrence, the characteristics of the virtual power ratio under different fault conditions are analyzed, and the fault protection strategy based on double-ended non-synchronous virtual power ratios is proposed. Finally, a four-terminal HVDC model is built in PSCAD/EMTDC to verify the fault detection performance under various fault situations. The results show that the proposed method can be adopted to achieve accurate identification of fault types with a sampling frequency of 20 kHz and complete fault detection within 1 ms. Meanwhile, it has a strong tolerance to transition resistance and noise, and has significant advantages over other methods.