Underwater spectral imaging technology plays an important role in underwater object recognition and ocean ecological monitoring. An underwater spectral imaging system using liquid crystal tunable filter (LCTF) was designed based on the actual engineering environment. The system obtained spectral information by using LCTF as a filter structure. Under the illumination of a wide-spectrum LED, a pool experiment was performed to obtain 31 channel spectral images of the target between 400 and 700 nm. The spectral information of objects with similar colors under water was discussed and analyzed. The results show that the system is helpful for underwater target recognition and classification. In-situ observation of corals in the sea trial successfully obtained underwater spectral images of coral reefs. The system is expected to be applied to ocean remote sensing, ocean ecological environment monitoring and other fields.