Composites of TiO2SiO2 oxides (CTS) with various Ti/Si atomic ratios were prepared by the solgel method, and the CO2 supercritical fluid extraction method was used to remove solvent in the gel. The effects of the Ti/Si atomic ratio and calcination temperature on the specific surface area, pore structure, acidity, and coordination status of the Ti atoms were investigated by N-2 desorption, pyridine adsorption, X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS), respectively. Hydrotreating catalysts were prepared with cobalt (Co)molybdenum (Mo) and nickel (Ni)tungsten (W) as active metal components supported on CTS-1 and CTS-4, respectively. The hydrotreating activities of the catalysts were tested by processing residue fluid catalytic cracking (RFCC) diesel on a fixed-bed reactor. It was found that hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodearomatization (HDA) were affected by the acidity of the support and/or catalyst, which was related to the Ti/Si atomic ratio. The catalysts with strong Lewis acidity had better hydrotreating activities for HDS, HDN, and HDA. The study provides insight into a fundamental understanding of the relationship between the Ti/Si atomic ratio of the support and acidity of catalysts and the effect of acidity on the hydrotreating activity of the catalyst.