the impovement and on-line adjustment of the monochromator of beamline 4B9A at BSRF were reported. The fixed beam exit of the monochromator and monochromatized X-ray intensity were tested. The results demonstrated that the indirect water-cooling monochromator is stable and mechanical instabilities are almost eliminated. It satisfies the experimental requirements of X-ray diffraction and Small Angle X-ray Scattering Stations at beamline 4B9A.