Dynamic characteristic is important to machine design and controller design of a permanent magnet synchronous machine (PMSM). In this paper, an experiment and corresponding test bench for estimating the dynamic characteristic of a PMSM is proposed, which is suitable for apply various variable load torque to the tested machine. The experimental platform consists of two PMSMs, one of them called tested machine and another is load machine. The tested one run in speed control mode and load one run in torque control mode. The load machine applied a sinusoidal torque load with variable frequency, amplitude and phase. Because load is sinusoidal, the tested motor is in motoring and generating alternating state. During the experiment, the experimental data of both the tested machine and load machine are recorded by a computer. It is found that by analyzing the experimental data, the tested machine and corresponding drive system can be able to accurately track the load torque and has excellent dynamic characteristics.