Cross-line current ratio fault location method is mainly applied to the all parallel power supply traction network (PSTN), including direct mode and AT mode, for the symmetry of the electrical parameters of the up-line and down-line traction network. To enhance the power supply capability of the PSTN, all parallel direct power supply mode is adopted in some China’s heavy-haul railways, and a reinforcing wire is in parallel with the heavy-haul side catenary, which results in asymmetry of impedance of the up line and down line. A simplified circuit model of the direct PSTN with asymmetric up-line and down-line impedance is built in this paper, and the adaptability of the cross-line current ratio fault location method in two traction network sections is analyzed. A modified scheme of the cross-line current ratio fault location method in traction substation—switching station section is proposed, and the original cross-line current ratio fault location method in switching station—sectioning post section is proved to be applicable. The simulation results based on MATLAB/Simulink show that the proposed modified fault location scheme can be well applied to this PSTN.