Eddy current retarder was a retarder braking set used in an automobile, and it can transform kinetic energy or mechanical energy of the automobile into heat energy, and heat energy was emitted around environment by the blades founded in the rotor of eddy current retarder, so flow field within the blade had direct effect on heat elimination and braking performance. In this paper two styles of 2D computational model for the rotor had been established. The flow field between and out of blades were analyzed by using RNG Κ-ε model and energy equation. The velocity distribution, pressure distribution between blades, static pressure on work face and rear face of the blade along radial direction all were accepted. The pressure, velocity and air flux for two styles of the blades had been compared. Numerical analysis of flow field was in favor of improved structure design for the blade.