According to the theory of signals and systems, the radiated system’s transfer function is derived, the radiation electromagnetic interference(EMI) simulation model of the wiper motor based on the finite integration technique(FIT) algorithm is established, and the whole system’s transfer function are obtained in the environment of simulation software CST. The terminal voltage of the motor，as the noise source of radiation system, can be gained with experiment. The radiation electric field can be calculated by transfer function multiplying motor’s terminal voltage. Then the complex question of motor’s systemlevel radiation can be transformed to the simple problems of computing system’s transfer function and the motor’s terminal voltage. By comparing simulation and experiment results, it is showed that the radiated EMI simulation model of the motor can demonstrate the essential feature of motor’s electromagnetic radiation system accurately, which means that it can be used in the research of wiper motor EMC forecasting.