The planet wheel gear deceleration box used for pumping sea water to cool off the neuclear power station has the characteristics of great input power, large volume and weight, low vibration and noise, long time to be used(continuously to circulate for 20 years) etc.. A local enterprise has used computer simulation for the research and development of the new product system, carried on sufficient pre technical design and analysis, using Pro/E software to establish the 3D model and assembly, dynamic motion imitation, using the Mechanica module belonging to Pro/E to carry on the FEM analysis. SimulationX software has been used for the vibration analysis. The pre simulation research and analysis have played a key role in the successful design and manufacturing of the whole new system.