The invention relates to a mobile substation technology, and in particular relates to a substation line interval replacement power supply method for a 110kV/3100A mobile high-voltage combination electric vehicle. The method comprises the following steps: in-place transportation of the mobile high-voltage combination electric vehicle, state detection of the mobile high-voltage combination electricvehicle, replacement of a patch cord by a line interval, communication set-up and debugging of the mobile high-voltage combination electric vehicle, monitoring parameter setting of the mobile high-voltage combination electric vehicle, and power supply and commissioning by replacement of the patch cord by the line interval. The power supply method is mainly used for transporting the mobile high-voltage combination electric vehicle to a substation when a substation line interval is overall overhauled or a main device fails; field alternative power supply and emergency rescue and disaster reliefcan be carried out; and thus, the power supply method has better practicability and reliability.