Abstract: Aiming at the design parameter optimization problem of Permanent Magnet Retarder (PMR),mathematic model of PMR electromagnetic field is made.Magnetic field and eddy current field in PMR are numerically solved by finite element method.The braking torque influence of rotor material conductivity,permeability and the plating layer is discussed,and the braking power formula that the rotor surface material has plating layer is presented.The simulation results show that: the electrical conductivity of the rotor is about direct proportion relationship with the braking torque when it is quite small,but with the conductivity increase,the braking torque becomes more and more saturated;rotor relative permeability has little effects on braking torque;the braking torque of the high-conductivity and non-magnetic rotor material is far less than the soft magnetic materials;plating layer can increase the maximum braking torque and the maximum braking torque move to the low-speed,but it will lead to faster decline in braking torque at high speed.