An Anomalous Surface Scattering (ASS) phenomenon was researched during the measurement of surface roughnesses for a smooth surface by a grazing X-ray scattering method. Firstly, an experimental facility based on an X-ray diffractometer were introduced. Several kinds of samples with different surface roughnesses were measured by an Atomic Force Microscope(AFM) and their surface scattering distributions in different grazing incident angles were given at working wavelength of 0.154 nm. Then, the relationship between anomalous scattering angles and critical angle was analyzed. Finally, the factors affecting on the scattering intensity were studied. Experimental results indicate that ASS can be observed when the grazing angle is larger than the critical angle. The anomalous scattering angle is related to the sample materials when incidence wavelength is a constant and it changes slightly with the grazing angle and surface roughness(Root Mean Square (RMS)). Moreover,all the measured anomalous scattering angles are slightly smaller than the nominal critical angle values of Si, fused quartz, Ni and Au respectively, and the measurement errors range from -8.6% to -0.9%. On the other hand, the equiangular reflection intensity is reduced obviously as the increasing of the grazing angle and surface roughness, whereas the intensity of ASS radiation is apt to increase instead of being weakened and the ratio of ASS peak intensity to equiangular reflection peak intensity ranges from 0.012 to 2.667. These results prove that sample materials and surface roughness are two principal factors affecting on ASS radiation distribution.