The invention relates to a method and system for judging an alternating-current line fault considering direct-current access. The method comprises the steps that positive sequence and zero sequence component amplitudes of the bus voltage at the two ends of a line are monitored, and protection is started if conditions are met; and zero sequence current direction angles and positive sequence currentamplitudes of the two ends of the line are calculated and substituted into a set formula to judge, and thus whether the line is a fault line or not can be judged. The fault line can be accurately judged.