The morphologies，chemical composition and crystal structure of the nanorod arrays on the sulfurated hydrorefining catalyst surface were studied by scanning electron microscopy(SEM),high resolution transmission electron microscopy(HRTEM),selected area electron diffraction(SAED)and X-ray energy disperse spectroscopy(EDS).The nanorod arrays were observed by SEM,which widely distributed on the catalyst surface.The nanorod arrays grew outward from the surface and assumed their regular shapes with lengths of 500-1 500 nm and diameter of 200-500 nm.According to the result of HRTEM,the nanorod arrays consisted of nanorods possessing single crystal structure with diameters of 40-100 nm.The image of crystal lattice fringe was also observed by HRTEM.The results of TEM-EDS showed that the nanorod arrays were composed of Ca,S and O.By means of the double tilt method,SAED patterns with different orientations were obtained.According to the chemical composition of the nanorod arrays shown by EDS and the crystallology information from the diffraction patterns of SAED patterns,the nanorods were confirmed to be of hexagonal calcium sulphate.The formation of calcium sulphate resulted from Ca originated from quartz sands which were mixed with catalysts in the fixed bed.Therefore,in order to prevent the generation of calcium sulphate,the quartz sands should be properly pretreated by calcining at high tempreture,acid cleaning and alkali cleaning,to eliminate the influence of calcium sulphate on catalytic activity in hydro-refining process.