Based on the application background of length measurement, a novel phase-shifting interferometry is presented. A precise phase-shifting device for length measurement by pressure variation is developed. This device based on single-quartz component is made to carry out the generation of triple phase-shifting, and an essential technique to make online calibration of the capacitor sensor is also realized. The original phase is solved by the developed five-interferogram algorithm with the uncertainty of 0.01% phase periods. The experimental results show that the phase-shifting obtained by this device is up to 1 μm and the variation for length measurement is 0.5 nm.