The utility model discloses a system for detecting the geologic structure of a shallow part of an optical fiber array seafloor. An optical fiber coil wound by optical fibers is used as a sensitive sonar sensor; two ends of each optical fiber coil are connected with optical fiber couplers; one of the other two ends of each optical coupler on the same side is connected to a single longitudinal mode laser device and the other end is connected with a photoelectric converter; the photoelectric converter is connected with a signal filter; the signal filter is connected with a signal amplifier; the signal amplifier is connected with an eight-channel signal sampler; the eight-channel signal sampler is connected with a computer; and a GPS time service instrument is connected with the eight-channel signal sampler. The system for detecting the geologic structure of the shallow part of the optical fiber array seafloor is a physical detector which is used for detecting the ground of a shallow layer of the seafloor, convenient to use, low in cost, long in signal transmission distance (a few tens of kilometers) and arranged on line; and the problem of seawater corrosion can be permanently solved.