In this paper, we investigate an underwater vehicle with two rudders suitable for working in Kuroshio near the eastern Taiwan, where the flow field of ocean current is less than 1.0m/sec. Lift and drag forces of the underwater vehicle submerged in the sea were calculated at different attack of angles and rudders by using finite element method. An on-site experiment with a prototype vehicle was also conducted located on Hsinta Fishing Harbor. Results show that lift force for the rudder of prototype vehicle near the sea surface is only 60% of theoretical calculations. To reduce the turbulence effect, the position of rudders in the front and the rear for the underwater vehicle should not be at the same level. Drag forces increase tremendously with increasing attack of angles compared with the effect of rudder's quantity. The power-free underwater vehicle has been built and controlled steadily at 0.6∼0.7m/sec flow velocity, suitable for carrying generators in Kuroshio.