Abstract: The support layout of the bed of a horizontal machining center directly affects the machine tool’s performance and assembly efficiency. Currently, most machine beds adopt multi-point support, which is prone to over-constraint and makes leveling difficult. Although three-point support offers convenient leveling, it suffers from insufficient support at the front end and large guideway deformation. To address these issues, a horizontally symmetric horizontal machining center is taked as the research object. Based on the orthogonal experimental design scheme and finite element analysis method, nine typical working conditions of moving components are selected, evaluation indices including the static and dynamic stiffness of the whole machine are constructed, and a method for determining the positions of four primary support points is proposed. The research results can provide a theoretical basis and reference for determining the primary support positions of high-end CNC machine tools.