Based on the terminal voltage difference of the opened phases in different circuits， a new method for identifying cross-line permanent fault on double-circuit transmission line is presented. When cross-line fault occurs， recovery voltages of the opened phases are studied and it is found that the terminal voltage difference is much different in the case of permanent fault and transient fault. The amplitude and phase of terminal voltage difference are both used for identification of permanent fault under the situation of different load current flows along the line. Simulation results demonstrate that the proposed method is reliable when applied in double-circuit transmission line on the same tower.