The operation principle and characteristics of flexible high voltage direct current (HVDC) is different from conventional AC and DC transmission. With the application of flexible HVDC technology, the fault characteristics of AC power system may change significantly, and the fault location algorithms based on conventional AC power system face challenges. Therefore, based on the operating principle of flexible HVDC, the operation characteristics of converter was analyzed when flexible HVDC/AC side has fault. The analytic expression of short-circuit current in AC side was derived with converter unprotected, current limited and converter blocked. The influencing rules of different transient operating conditions on the performance of single-terminal fault location for transmission lines were analyzed. It is concluded that the performance of single-terminal fault location for transmission lines in an HVDC/AC interconnected power system is influenced by the converter-side voltage dip coefficient and the referenced reactive power of the converter. And the correctness of theoretical analysis is verified by PSCAD/EMTDC simulation.