This paper presents a new two-terminal asynchronous fault location method for modular multilevel converter based high voltage direct current(MMC-HVDC)transmission line. Firstly

by analyzing the current path of the MMC-HVDC system under line fault

the two side loops of the two-terminal MMC after tripping are equivalent to RLC series circuits. Then the two-terminal MMC bridge submodules are put in

which provide initial voltages for the RLC series circuits. According to the zero-input response characteristics of RLC circuit

the maximum value of the capacitor current and the corresponding capacitor voltage of the two-terminal MMC submodules are obtained respectively. Finally

the fault distance is calculated by using the asynchronous measurement data. The method does not depend on the initial capacitor voltage and is not affected by the transition resistance

and the fault distance can be measured repeatedly which can improve the reliability. A 21-level MMC-HVDC model is built by PSCAD/EMTDC

and the simulation results show that the proposed fault location method is effective.