SX-700 monochromator is the key part of the Shanghai Synchrotron Radiation Facility soft X-ray spectromicroscopy beam-line，whose important subassembly is the grating sine mechanism. Difficulty is that the angle repeatability of the grating sine mechanism must be less than 0.43”. To prove the design of the grating sine mechanism could meet the requirement

the error sources that affect the precision of the wavelength scan are construed; and the numerical simulation for the sin-bar and drive rod of the sine mechanism are done by using the finite element software ANSYS。The error analysis for the rotation-angle-accuracy of the grating sine mechanism is done according to the results of the numerical simulation

and the rotation-angle-accuracy is 0.28”. The angle repeatability of the grating sine mechanism is measured with an autocollimator system designed by us

and the angle repeatability is 0.15”. The result reveals that the structural design of the grating sine mechanism fulfills the design requirement of the angle repeatability.