As one of the key technical solutions for nano-displacement measurement, the interferometric grating displacement measuring system has such characteristics as high precision, high resolution and small size. Because the interferent light beams come from the diffraction of gratings, the system is sensitive to gap and rotational tolerance between the optical head and scale, and is difficult to align. A symmetrical double-grating interferometric displacement measuring system, which achieves high-precision displacement measurement, is developed based on optical effect of Doppler shift and circularly polarized light interference. The system has small tolerance and simple alignment. The performance tests show that the developed system has the actual resolution of 0.8 nm, repeatability of 1.4 nm. In the movement range of 1-14.5 μm, its accuracy without correction is 15.4 nm, and the accuracy with trajectory error correction is 5.5 nm. After periodic error correction, the accuracy can be improved to about 1.4 nm.