High accuracy linear movement in grating monochromators of synchrotron radiation beamline is essential.Usually the linear displacement accuracy requirement is about 1 micron to achieve the spectral resolution.A laser interferometer and an autocollimator are used Beijing Synchrotron Radiation Facility(BSRF) to measure linear displacement of the mechanism and to calibrate the linear encoder.It measures not only precision of the linear displacement

but also linearity of the movement.Linear displacement mechanism was tested by the system with accuracy of 1.0×10-3 mm and resolution of 7.5×10-5 mm.The linear encoder can give the displacement at an accuracy of RMS=3×10-4 mm within 160 mm range.This system plays an important role for both linear displacement mechanism commissioning and for wavelength calibration of the monochromators.