The crystal monochromator is a key device of the X-ray beamline. It uses crystals as dispersive elements to diffract and separate the synchrotron radiation

and provide X-ray monochromatic light with a given energy bandwidth. Using a pair of Si (111) crystals with (

+

n

-

n) arrangement

the double-crystal monochromator mounted on Hefei facility can assure the parallel of the crystal surfaces and provide a spatially fixed monochromatic beam only by a simple Bragg rotation with a special L-mould linkage mechanism in the course of energy scanning. The focus of the paper is the energy scanning mechanism of Hefei crystal monochromator.