Abstract: Random perturbations exist in the working environment of submarine optic fiber cable, so using traditional single-pulse TDR to detect the fault of submarine optic fiber cable sheath can not get ideal waveform due to the interference of random noise, and fault detecting effect is unsatisfactory. To solve this problem, an equivalent circuit model of submarine optic fiber cable sheath was proposed based on the structural characteristics of submarine optic fiber cable sheath, which is equal to a lossy-nonuniform transmission line with random perturbations. And a fault-detecting method was put forward, which adopted unipolar coding pulse as detecting signal. Through theoretical analysis and experimental studies, this program can effectively reduce the nosie of system without reducing the spatial resolution and improve the system gain compared with single-pulse TDR. So the detecting result can be improved, and meet the requirements of submarine optic fiber cable sheath fault-detecting engineering.