Based on analysis of several main arrangements of same-pole double-circuit transmission line（SDTL） and unbalanced current phenomenon， a fault caused by zero-sequence power directional component mal-operation resulted from over threshold value of zero-sequence circulating current， when an external inter-phase fault happened in EHV SDTL， is analyzed. Then the analysis method of zero-sequence circulating current unbalance of SDTL is given. And a simulation of zero-sequence circulating current unbalance for an external inter-phase fault on SDTL is completed with EMTDC. As for mal-operation of SDTL directional pilot protection caused by zero-sequence circulating current， the improvement measures of SDTL's directional pilot protection based on the sequence components is put forward.