The central and western regions of China are located in high-intensity seismic zones, with some areas having a seismic fortification intensity as great as 9-degree, posing great challenges to structural seismic design. This paper takes a high-rise elderly-care building structure in a 9-degree seismic fortification area in western China as an example, focusing on the combined seismic isolation and seismic mitigation design method of steel structures. We compare 3 design schemes: Conventional steel structure scheme, seismic isolation scheme, and combined seismic isolation and seismic mitigation scheme, where lead rubber and natural rubber bearings as well as viscous dampers are arranged in the isolation layer, and buckling restrained braces are arranged in the upper structural steel frame. In comparison, the combined scheme yields the best seismic reduction performance, and the seismic response of the upper structure is significantly reduced. The result analysis of the base shear force, upper structure deformation, tensile stress of isolation bearings, and energy dissipation of typical components shows that this combined design method for the high-rise building is feasible, and all calculation indexes can meet the requirements of Chinese design codes, providing references for similar high-rise buildings in high-intensity zones.