A system used for testing transient velocities and displacements of the micro-electronic-mechanical system (MEMS) devices is presented. A differential laser Doppler technique is adopted to measure the in-plane vibration of MEMS resonator and vibration velocity which is perpendicular to the optical axis of the measuring system. A CCD camera with imaging system to observe the position adjustment and resonator vibration status is introduced to the optical arrangement. The Doppler frequency is extracted by processing circuit from the high-frequency output of the optical system, and powerful Labview & Matlab are used in time-frequency analysis to measure the movement parameters. In the system, a tiny location device is used to scan the whole plane of the MEMS devices. As a result the transient velocity field, which provides certain basis and necessary support for the higher-order spectral analysis and torsion analysis, is achieved.