Interval identification and accurate location of faults on the DC side are important issues that need to be resolved urgently for a multi-terminal flexible DC grid. This paper uses the current characteristics of bipolar short-circuit faults and proposes a fault interval identification method based on the Pearson correlation coefficient. Given the maximum value of the current after the fault and its corresponding voltage value, a fault location method based on double-ended asynchronous electrical quantity data is proposed. A line protection scheme including fault initiation, fault zone identification, fault location, and fault isolation is designed. This scheme realizes line protection by measuring local electrical quantities, and has strong tolerance to transition resistance and anti-disturbance capabilities. A four-terminal flexible DC transmission system is built on the PSCAD platform, and a large number of simulations have verified the applicability and accuracy of the fault zone identification and fault location scheme proposed in this paper. This work is supported by the National Natural Science Foundation of China (No. 51767014 and No. 51867013).