The invention relates to a method for calculating the sheath current of a single-core cable, aiming at accurately calculating the sheath current of the single-core cable and providing guidance for reasonably configuring the sheath current and reactive power for laying and transformation of the cable. The method comprises the following steps: (1) determining the radius a of a cable core, the outerradius b of an insulating layer, the relative dielectric constant Epsilon, the relative permeability [mu]0 of the insulating layer, the resistance Rt of a cable sheath and the conductivity gamma of the insulating layer according to cable parameters; (2) determining a cable length l, a power supply voltage level Us, a power supply frequency f, a power supply voltage level Us and a cable grounding end grounding resistor Rd according to cable operation conditions; 3, calculating capacitive current IC of the single-core cable sheath; (4) calculating the inductive current IL of the single-core cable sheath; 5, calculating the resistive current of the single-core cable sheath; 6, calculating single-core cable sheath current through the following formula I: I =-j (IC+IL)+IR.