Currently, fault detection and location of submarine cable in seafloor observation network is affected by fault resistance, natural environment and climate. The seafloor observation network's submarine cable failure is difficult to detect and locate, thus bringing many obstacles to underwater maintenance. Aiming at the defects of current fault location methods in seafloor observation network, a fault location method based on multi-terminal traveling wave is proposed for the first time in this paper. Firstly, the fault line is determined with intelligent branch unit (BU), and the shortest transmission path of the initial fault traveling wave head is calculated with Floyd algorithm. Secondly, the submarine cable is divided into several equipartition sections, and the distances from each equipartition point to each line end point and connecting point are calculated. Then an initial traveling wave path matrix is constructed, and the reference traveling wave head arrival time difference matrix is established based on the traveling wave velocity. After the fault, a time difference matrix is established using the times the traveling wave heads arrive at the fault point, measured with the synchronous measuring device installed at the end of each line. Finally, the fault location is determined using the difference of the time difference matrix before and after the fault. PSCAD simulation proves that the proposed method is simple to implement and accurate in positioning, providing guarantee for safe and reliable operation of the submarine observation network power system.