In order to improve the precision and quality of electrochemical machining of complex surface/cavity parts, the design of horizontal electrochemical machine tool which can realize the compound feeding motion of straight line and rotation was carried out. Under the impact of large processing current and high-speed electrolyte, the machine tool needs to have high stiffness to withstand dynamic and static loads. In this paper, UG software is used to build three-dimensional model of horizontal machine tool, and the simplified model is imported into ANSYS Workbench software for static analysis. The structural stiffness of the machine tool is analyzed based on deformation and stress distribution nephograms. The first six natural frequencies and modes of motion platform are determined by modal analysis, and the optimal design is carried out by using the variable density topology optimization method. Finally, the design is redesigned on the basis of considering the technological characteristics of the structure, and the lightweight design goal is achieved. The designed ECM machine tool has sufficient stiffness and stability, and can meet the requirements of actual processing.