A numerical simulation method of the motion of a rowing race boat is developed in order to evaluate the performance of oar size and rowing pattern. The driving force of blade is measured experimentally. The resistance of the boat is referred to the experimental result carried out in a towing tank. The motion of crew, which is most important in the simulation, is evaluated from the equation of a boat motion where the other terms are experimentally measured. These measured external forces are modeled by Fourier series or polynominal expressions. The equation of a boat motion is numerically solved by use of Runge-Kutta method. The Simulated boat velocity and force acting on blade are compared with the measured ones. The experiment was carried out in cooperation with the crew at Hiroshima University. Good agreement with the simulated results and measured ones shows that the present simulation method has merit to evaluate the rowing performance. Through the present simulation method, outboard length, blade area, stroke rage and phase of catch are evaluated.