Abstract: An defect detection method of micro-cantilever beams based on optical coherence vibrometer (OCV) system was proposed. The maximum vibration displacement measuring range and vibration frequency of the home-made OCV system were 2.574 mm and 138.5 kHz, respectively. This system was used to carry out the vibration measurement of the defective micro-cantilever beams with additional mass-block coupled structure, and its natural frequencies were obtained. Subsequently, the defect location was realized by using the influencing characteristic of the additional mass-block on natural frequencies. In the process of processing the interference spectrum signals collected by the system, the fast Fourier transform (FFT) and Fourier transform (FT) refinement spectrum correction algorithm was utilized for error correction, and the accuracy could be increased by more than 1 000 times, which enabled the system to realize the displacement measurement at nanometer scale. The experimental results show that this method can identify the defect location of micro-cantilever beams effectively, which provides a new method for the defect detection of micro structures and expands the application of optical coherence vibrometer technology in nondestructive testing of engineering structures.