The invention discloses a cable buffer layer conductivity defect detection method which comprises steps of electrically modeling a cable, disposing a resistor and capacitor between the wire core and the metal sheath of the cable to be detected, connecting one end of the wire core to test voltage, suspending the other end of the wire core or disconnecting the other end of the wire core from a load,suspending one end of the metal sheath or grounding the one end of the metal sheath through a voltage protector, and directly grounding the other end of the metal sheath; applying an AC test voltageto the wire core of the cable, and recoding the test voltage and the no-load test current waveform of the directly grounded end of the metal sheath; according to the basic parameters of the cable andthe test voltage, calculating the no-load theoretical current waveform of the directly grounded end of the metal sheath; comparing the phase and the amplitude of the no-load theoretical current waveform with those of the no-load test current waveform, and determining that the cable buffer layer has a conductivity defect if a set threshold is exceeded. The cable buffer layer conductivity defect detection method detects the entire cable, is simple and high in efficiency, and solves the inability to detect the cable in operation.