Abstract: Underwater soft actuators play an important role in underwater biological sampling, cultural relics salvage and other operational tasks, but their proprioceptive ability is insufficient. One reason is that traditional underwater sensing modules are unsuitable for soft actuators, and are susceptible to ambient temperature, with poor anti-interference ability, large volume, and large hardness. In order to solve this problem, a proprioceptive function of a bellow-structured soft actuator is developed based on a flexible optical waveguide sensor, which is insensitive to temperature and electromagnetic interference and is of a fast response speed and high linearity. Firstly, the soft actuator's ability to detect basic physical properties of objects (surface texture and hardness) is tested in the laboratory shallow water environment. Secondly, the application feasibility of the soft actuator in typical operation scenarios of 3000 m underwater is preliminarily verified in a laboratory simulated static water high-pressure environment (0~30 MPa). The experimental results show that: the soft actuator can sense the sawtoothcorrugated surface with an amplitude of 1 mm at a driving pressure of 40 kPa in the shallow water environment; when the driving pressure is greater than 30 kPa, the soft actuator can clearly distinguish the bending state of the body and three objects with different hardness; under the hydrostatic pressure 0~30 MPa, the flexible optical waveguide sensor can well characterize the soft actuator's different bending states; when the water pressure rises, the hysteresis of the sensor increases, and the sensitivity decreases. The above experimental results show that the proprioceptive soft actuator based on the flexible optical waveguide has the function of underwater in-situ perception, and still has good perception performance in the equivalent underwater 3000 m operating range.