Micro displacement is precisely produced either directly by squirm movement, or indirectly by the enlargement effect from the lever with microstructure, driving by the external force, electric field or magnetic field on the micro displacement devices. For example, the piezoelectric transducer is driven by the voltage, to squirm with micro displacement, based on the converse piezoelectric effect. In this article, we summarize measurement and calibration methods of micro displacement of the PZT used as phase shifter of the interferometer to guarantee a phase-shifting step of λ/8(λ=632. 8nm), based on the researches of our group in recent years. The precise positioning with resolution better than 10 nm is achieved by displacement sensing utilizing the feedback of a capacitor on the PZT.