Electromagnetic field analysis for permanent magnet type eddy current retarder is the key part for designing. In order to research electromagnetic field distribution of the retarder, permanent magnet was made equivalent to a magnetized current. Flux density and eddy-current density in the air-gap and rotor of retarder were analysed and calculated respectively based on Rogowski method; meanwhile,the computation formulae of its braking torque were derived in order to reflect the relationship between braking torque and different design parameters. The analytical model was proved to be an effective model that can reveal the essence of electromagnetic field of permanent magnet type eddy current retarder, and the comparison of bench test result and computation result shows that the maximum error is less than 10%, which means Rogowski method is effective.