The velocity vector around a horizontally submerged circular cylinder in the vicinity of channel bed was obtained by visualization method and then corrected to have higher accuracy by calculus of variation under the constraints of the continuity equation. The stream function and the vorticity distribution were determined as well as the pressure distribution according to an unsteady Navier-Stokes equation. The position of each separation point on the channel bed and the vortex formation factor were determined to obtain essential data in the method of discrete vortices.