The invention discloses a full-fiber current transformer fault diagnosis method and device. A method for collecting the peak value, the valley value and the secondary harmonic amplitude of the outputwaveform of a detector in a normal operation state and a fault state is adopted, and by comparing the size of the parameters in the two states, the fault diagnosis of an all-optical-fiber current transformer which is modulated by sine wave is divided into a light path fault, a modulation loop fault and a measured current fault, and fault removal is carried out under three conditions according to the diagnosis result. The fault diagnosis method is reliable and effective, a method guide is provided for the fault removal of the all-optical-fiber current transformer for sine wave modulation, the fault removal rate is high, and the operation reliability of the all-fiber electronic transformer in a converter station can be remarkably improved.