A new generalized modular design (GMD) method is proposed based on design practice of frame structure of hydraulic press machines. By building a series of flexible modules (FMs), design knowledge and structure features are integrated into parametric models. Then, parametric design and variational analysis methods for GMD are presented according to user defined design objectives and customized product characteristics. A FM-centered GMD system is developed and successfully used in the rapid design of relevant products. A new generalized modular design (GMD) method is proposed based on design practice of frame structure of hydraulic press machines. By building a series of flexible modules (FMs), design knowledge and structure features are integrated into parametric models. Then, parametric design and variational analysis methods for GMD are presented according to user defined design objectives and customized product characteristics. A FM-centered GMD system is developed and successfully used in the rapid design of relevant products.