The invention relates to an interturn protection method of a TCT type controllable high-resistance triangular connecting winding and belongs to the technical field of relay protection of power systems. The method comprises the steps of measuring a high-voltage side zero sequence voltage U0 and comparing with a setting value U0set; measuring line currents iA(t), iB(t) and iC(t) of the TCT type controllable high-resistance triangular connecting winding and resolving vectors; calculating third harmonic positive-sequence component I3+(alpha) in the currents of the TCT type controllable high-resistance triangular connecting winding; when U0 is smaller than U0set and I3+(alpha) is larger than I3set, judging that an interturn fault exists and outputting a tripping signal; performing protection without action when any one of the two conditions is not met. By using the difference between the contents of the third harmonic positive-sequence component in the currents of the TCT type controllable high-resistance triangular connecting winding during the interturn fault and normal operation, on one hand, the problem of the insufficient protection sensitivity of the traditional zero sequence power direction is effectively solved, and on the other hand, only line currents outside the triangular connecting winding need to be measured without referring to the problem that the current in a three-phase one-body structural angle cannot be measured, so the interturn protection method has actual engineering significance for the TCT type controllable high-resistance protection and configuration.