In this paper, prism beam-splitting structure is proposed in the design of optical system to solve the problem of full-color imaging under low-light environment of the deep-sea. Optimization of optical aberrations is performed considering the specific aberration properties of the sea water and the window materials in the optical system. The designed optical system (field of view 60 degrees and F/4) shows a clear imaging for all fields of view where MTFs is over 0.5 (@77lp/mm). The optical performance demonstrates that the system is very promising for large depth of field and full-color imaging under deep-sea environment.