Abstract: Product performance,as the core of product design,governs the design activity throughout the entire process.How to describe product performance,in a sense that how to capture the commonness of product design is a challenging task.Based on factor space theory and tertiary level reconciled functional basis,a description framework for performance factor is proposed using the unified functional taxonomy representation as dimensional tag.A five-step process of bringing a performance factor into framework space is described in order to clarify the concept of performance factor space.In addition,the space characteristics of the presented framework are addressed and some important conclusions are obtained.The performance factor space not only offers an abstract presentation room for product performance,but also provides reference coordinates for its quantitation,based on which an approach of product retrieval by performance indexing is hopefully achieved and hence,the CAD technology may be promisingly applied in the earlier phase of product design so as to bridge the gap between conceptual design and detail design.