Most of the double-circuit lines on the same pole are not transposed continuously， which may cause inter-line coupling. Based on the decoupling transformation， a differential current expression is described for double-circuit line， and the differential current characteristics of all the phases are analyzed for both in-zone simple faults and inter-line faults. It is shown that the unbalanced differential current of the non-fault phase for the double-circuit line is larger than that for the single-circuit line. Therefore， a countermeasure is taken， and a practical protection scheme for the double-circuit line is presented which can be implemented on the basis of the fiber-optic channel available for the fast and sensitive operation provided while avoiding mal-operation during external faults and in unloaded switching conditions. The results of simulation corroborate the applicability of the scheme.