In order to realize the multi-point load measurement of ship hull during wave experiments, an FBG pressure sensor was developed to monitor ship bottom liquid level. The principle is to measure the responses of optical fiber sensing units caused by hydraulic pressure. By utilizing a designed steel diamond structure and reasonable selected material, the sensor realized the temperature self-compensation function of a single FBG. The theoretical models and experimental methods are analyzed in detail. Lots of sensing tests showed that, the sensor had a sensitivity of 58.94 pm/kPa and a precision of 1.7 Pa. The temperature sensitivity was only 2.7 pm/°C, which basically achieved the effect of temperature self-compensated. Finally, 15 sensors were installed at the bottom of the hull and a series of wave load experiments were carried out, which further showed that the pressure sensor had good measuring ability and wide application prospect.