Dynamic population gratings recorded in rare-earth-doped optical fibers, which are promising substitutes of photorefractive crystals for adaptive interferometric detections of mechanical vibrations and laser-induced ultrasound especially in industrial conditions, is formed by two counter-propagating mutually coherent laser recording waves via local saturation of the fiber optical absorption or gain (in optically pumped fibers). The dynamic population gratings are very attractive for different applications such as single-frequency cw fiber lasers, tunable narrow-band fiber optical filters, fiber optical sensors, adaptive interferometers, etc. The detection configuration will have an all-fiber design and will be based only on commercially available elements. In this work, we report an optical fiber adaptive vibrometer based on dynamic population grating in Er-doped optical fiber. A linear interferometer utilized for adaptive detection of mechanical vibrations. The two-wave mixing signal appears here as a result of nonlinear interaction between the direct wave R and the back propagating phase modulated wave S, which is reflected from the vibrating surface of a piezoelectric vibrating mirror. This all-fiber detection system has a fast response, is easy to prepare, which can be a potential method for detection of mechanical vibrations.