This paper describes the laser interferometer which can measure automatically both the1ength gratings up to 2m (grating linear displacement sensors) and the line standards up to 1m. Theinterferometer was designed according to the Appensfein principle which can offset the Abbe Errorcaused by the method of fitting the length grating during measuring it. The length of the line standardsand the length gratings using fringe counting theory can be measured, and also the quality parameters ofgrating signal with this instrurnent be analyzed. ln the course of measurement, the refractive index ofthe air around the interferometer was corrected real time.