This paper presents a research on the development of an innovative product design method with an aim to consider the energy-saving issue throughout the entire product life cycle. The research is based on a comprehensive analysis of regular product design procedures to extract the design information that correlates with energy consumption, itemize and quantify the information, and eventually build up mathematical models for final optimization. The result of this research will be used as guidelines for regular product design and achieving energy-saving design result. The objectives of the research are in three-fold: (1) establishing a mechanism that can explicitly demonstrate the product design information that includes energy consumption throughout all stages of product life cycle; (2) modeling energy parameters with quantitative mathematical expressions; (3) developing a decision making system to optimize product design in terms of energy-saving. A concept called Design Unit (DU) will be introduced as a new method to describe product design information related with energy consumption. The axiomatic design theory will be integrated with DU concept, and becomes an important standard for optimizing product design. An new concept called Energy Factor will be introduced briefly in this paper.