Abstract: In order to heighten the manipulative accuracy of the ruled engine,a new measurement system auto-collimating grating heterodyne interferometer was proposed.Based on the diffraction and polarization of grating and some theories of the electronics,the system was analyzed.After the benchmark grating was designed,and lots of experiments were carried out.Because the interferometer measurement system takes grating constant as the measurement standard,the effect of environment on measurement accuracy is reduced.Thanks to the auto-collimation diffraction,the structure is simple and steady,and easy to assemble and adjust.Moreover,using the dual-frequency,high gain and signal-to-noise ratio can be obtained.Using the interferometer system to control the ruled engine,the biased error for ruling span is less than 10nm,and the cumulative error is about 0.3μm within 3mm displacement.The results show that the resolution of the interferometer system is small to nm scale,and it can be used in the real-time measurement control system and that it achieves high accuracy that the special diffraction gratings such as echelon gratings request to a ruling engine completely.