Provided is a design method for a support structure of a large-scale vibrational excitation platform. The present invention designs a dimension of a support structure matching a dimension of the vibrational excitation platform, selects appropriate materials to guarantee structural stiffness, performs simulation and verification of finite elements to verify a natural frequency and stress deformation of the support structure, breaks down the support structure to facilitate processing, transportation and assembly, and optimizes structural parameters to enhance stability and stiffness of the support structure. The support structure designed using the design method in the present invention features strong stability, simple structure, high natural frequency and easy to mount. The support structure is assembled by means of welding and threaded connections, and is reinforced with reinforcement plates at important parts, such that structural stiffness and strength of the support structure are guaranteed.