Testing the dynamic characteristics of the wheel-hub motor has important applications, due to the motor′s wide use and significant role in the performance of electric vehicles. By analyzing the working principle of a permanent magnet DC (direct current) dynamometer system, a frame-type mechanical structure of the dynamometer was designed that uses double universal coupling to connect the output shaft of the generator, torque and speed sensor, and input shaft of the testing motor. Moreover, by using the vice-transmission of a pair of external meshing gears, the mechanical transmission link between the generator and the measured motor was established. Based on the PWM (pulse-width modulation) signal, the loaded circuit of the DC dynamometer system was designed that substitutes the real load for an equivalent simulated load. In this way, the wheel-type permanent magnet DC dynamometer system was constructed. The experimental results showed that it had a simple structure, was easy to control and use, and had stable and reliable performance that meets the needs of the testing wheel motor. It can thus be used for dynamic performance testing of the small disc brushless motor.