本文介绍了我们研制的用于位移精密测量的光外差马赫－泽德干涉仪。由于在光路设计中采用了共光路的布置，共模抑制技术得以实现，环境干扰产生的噪声得到很好的消除，相位检测的稳定性和精度大大提高。使用该干涉仪测量了一台在光学相移器内ＰＺＴ微位移驱动装置的电压－位移关系。测量结果具有良好的线性和重复性，与预期相符。根据测量数据分析，该光外差干涉仪具有３ｎｍ的位移测量精度。 This article describes the optical heterodyne Mach-Zehnder interferometer we have developed for displacement precision measurement. Since the common optical path is used in the optical path design, the common mode rejection technique can be realized. The noise caused by the environmental interference is well eliminated, and the stability and accuracy of the phase detection are greatly improved. The interferometer was used to measure the voltage-displacement relationship of a PZT micro-displacement drive in an optical phase shifter. The measurement results have good linearity and repeatability, in line with expectations. According to the measurement data analysis, the optical heterodyne interferometer with 3nm displacement measurement accuracy.