As a kind of underwater detecting technology, hyperspectral imaging technology has been well applied in many areas. But the systems usually have a large volume, and it is hard to mount them on different platforms because the external scanning mechanisms are needed for scanning imaging. To overcome these disadvantages, an underwater hyperspectral imaging system that achieves scanning imaging through moving the objective lens is designed. The design of the optical system and internal scanning and focusing structure were completed. According to the design result, the system is assembled and tested. The imaging quality of the whole system is good, and the obtained spectrum of different targets can be distinguished. The system has a good underwater detection capability, which can provide a new feasible technical scheme for underwater detection.