Currently, Energy and Environmental issues are worldwide concerns. Energy savings is also without doubt the most effective strategy for environmental protection. This paper introduces a new general product design method. Our research effort will be directed towards the following three primary objectives: (1) investigating all the aspects related to energy-saving issues throughout the entire product life cycle; (2) developing a mathematical model (called Energy Factor) to calculate the products' energy consumption throughout the entire life cycle; (3) establishing the theoretical frame of the new innovative product design method. In this innovative method, the energy-saving concept will be applied at the first step of product life cycle, i.e. product design. And we believe that it will bring the product design to a new stage, which can design the energy-saving products and manufacturing systems. In order to reduce the energy consumption throughout the entire product life cycle (from cradle to grave), this design method is based on axiomatic design theory, and integrates design unit and energy factor concepts. In this paper, the theory frame will be described in detail, and the new concept called energy factor will be introduced briefly.