An autonomous underwater robot equipped with a manipulator is expected to play an important role in future ocean development such as repairing marine cables, constructing offshore structures and removing seabed sediment. In order to make it fit for practical use, an effective control method for the manipulator in the presence of hydrodynamic effects needs to be developed. In general, control methods for mechanical systems are validated by simulation and/or experiment. A simulation study is cost-effective in comparison with an experimental one, especially in such an expensive system as underwater robot that requires a huge tank, waterproof robots, and so on. In this report, we develop a simulation system for underwater robot manipulators by means of the computer software MATLAB/Simulink. Since the software is widely used in the field of control and robotics and has many tools for controllers, the underwater robot simulation system developed in this report facilitates confirming the effectiveness of a control method for underwater robot manipulators.