The present invention discloses a dual-sampling and dual-demodulation fault alarm device and method used for an optical fiber current transformer. In the device, two AD modules sample the detector signals parallelly, the sampled data is demodulated simultaneously and independently via a demodulation module, after the demodulated current signals are added and averaged, a DA conversion circuit applies to a Y-waveguide modulator to realize the enclosed loop control, at the same time, the current signals are demodulated and obtained simultaneously to output separately, thereby realizing the electric power application dual-configuration demand. The data alternatively sampled by the two AD modules within a same modulated amplitude is compared and determined to give out an AD fault alarm signal, and the current signals obtained by carrying out the signal demodulation on the data sampled by the two AD modules simultaneously and independently are compared to give out a demodulation module fault alarm signal. According to the present invention, on the condition of not increasing the light path complexity, the dual-configuration output and the fault alarm functions of a core device and a modulation and demodulation module are realized, the structure is simple, the cost is low, and the intelligent degree is high.