Laser Doppler vibrometer can measure the displacement, velocity, acceleration and other parameters of vibration target. It has the characteristics of non-contact, high precision and long distance. So, it has a great advantage for the vibration measurement in a special working environment, where the target is light and thin, hard to contact, hard to approach. Laser heterodyne interferometry is an important means of detecting the micro vibration. With the development of micro vibration application, the sensitivity of phase measurement is highly required. Traditionally, there are several ways of improving the measurement sensitivity, such as optimizing the heterodyne interference scheme, improving the phase reconstruction algorithm and reducing the noise of key devices and so on. However, based on the analysis of the influence of stray light in the system, it is found that the controllable multi-beam interference can greatly improve the detection capability of the system. Therefore, a phase enhancement technique of multi-beam hybrid interference is proposed to meet the needs of high sensitivity detection of micro vibration. In this paper the physical mechanism and boundary conditions of phase enhancement are investigated in detail, and the quantitative relationship between the boundary conditions and phase enhancement is also analyzed thereby providing a technical reference for the enhancement detection of micro vibration targets. Through the numerical simulation and experimental verification, the following boundary conditions are obtained: the initial phase difference between the correction light and the signal light is π rad and the closer the power values of the two beams, the greater the enhancement effect of the demodulation phase is. The power difference between the two beams designed in the experiment is 1%, which means that detection capability is enhanced by 146 times. It has great application value in the high sensitivity measurement of micro vibration objects. This technology can also enhance the detection capability of heterodyne interference measurement system without changing the existing device index or phase demodulation algorithm.