A new method for spectroscopic interferometry using rotating diffraction grating was developed for industrial measurements. Two diffraction gratings increase the spectroscopic resolution, and the effective measuring range can be extended considerably. Instead of calibrating the wavelength, we used the Fabry-Perot Etalon (standard) to calibrate the system and determine the absolute position. The rotation diffraction gratings may also be used as a spectroscopic element over extensive ranges for low-cost and high-speed measurement. Our experiments indicate a length range of approximately 4.00 mm with repeatability of 0.17μm (0.0167%) for the narrow range and 3.84 μm (0.0955%) for the wide range.