A stroke-analysis system based on a CFD (Computational Fluid Dynamics) simulation has been developed to evaluate the hydrodynamic forces acting on a swimmer’s hand. Using the present stroke-analysis system, a stroke technique of top swimmers can be recognized with regard to the hydrodynamic forces. The developed analysis system takes into account the effect of a transient stroke motion including acceleration and a curved stroke path without using assumptions such as a quasi-static approach. An unsteady Navier-Stokes solver based on an unstructured grid method is employed as the CFD method to calculate a viscous flow around a swimmer’s hand which can cope with the complicated geometry of hands. The CFD method is validated by comparison with experiments in steady-state and transient conditions. Following the validations, a stroke-analysis system is proposed, in which a hand moves in accordance with a stroke path measured by synchronized video cameras, and the fluid forces acting on the hand are computed with the CFD method. As a demonstration of the stroke-analysis system, two world class swimmers’ strokes in a race of 200 m freestyle are analyzed. The hydrodynamic forces acting on the hands of the top swimmers are computed, and the comparison of two swimmers shows that the stroke of the faster swimmer, who advanced at 1.84 m·s^-1 during the stroke-analysis, generated larger thrust with higher thrust efficiency than that of the slower swimmer, who advanced at 1.75 m·s^-1. The applicability of the present stroke analysis system has been proved through this analysis.