A method for identifying and measuring the hidden defects of optical cables based on Brillouin optic time domain reflectometer (BOTDR) distributed detection technology and demodulated signals was proposed to identify and measure the hidden defects of optical cables and ensure the safe operation of multi-strand carbon fiber optic cables used in projects such as capacity expansion and large span. In the production stage, the optical fiber was embedded in the composite core of multi-strand carbon fiber cable as a sensor. According to the principle of BOTDR technology and optic time domain reflectometer (OTDR) technology, a distributed sensing system for the detection of the hidden defects of carbon fiber cable was constructed. The hidden defects and position distribution of carbon fiber cable were analyzed in a multi-dimensional way by using the high-precision sensing of the optical fiber on temperature, stress and propagation loss, which realized hidden defect identification of optical cable. The Morlet wavelet was used to demodulate Brillouin scattering signal, extract envelope information and remove signal noise. Levenberg-Marquardt algorithm was used to fit Brillouin scattering spectrum data, accurately estimate the optimal Brillouin frequency shift parameter, and improve the overall defect recognition accuracy. The experimental results show that this method can accurately characterize the hidden defects of optical cable, realize the fast and effective identification of hidden defects of multi-strand carbon fiber cable, and promote the better application of carbon fiber cable in capacity expansion, large span and other projects.