We investigate the three-beam conjugate enhanced micro-vibration detection system. We introduce a conjugate light to the classical dual-beam heterodyne laser vibrometer to generate the three-beam interference. Detection of the micro-vibration signal is then enhanced by matching the power and phase of conjugate light and measured light. We also present the basic principle of three-beam conjugate enhanced micro-vibration detection and the conjugate enhancement conditions. Moreover, the expressions of micro-vibration signal amplitude amplification and resolution enhancement are derived and compared with the demodulation amplitude and limited resolution of classical dual-beam laser vibrometer. Experiments and numerical results further verify the amplitude amplification and resolution enhancement of the three-beam conjugate enhanced micro-vibration system. The archived results indicate that this system is especially suitable for the high-resolution detection of weak vibration targets, e.g., micro-nano structures.