The work aims to propose an extended model of product concept design that integrates demand analysis and appearance coding to improve the usability of the elderly-oriented products. Firstly, literature analysis was used to understand the research on usability design of elderly-oriented products and the development status of classical conceptual design models. At the same time, combined with the value of appearance in product semantics to convey product functions and operation modes, a new idea was proposed to apply product appearance coding to improve the usability of the elderly-oriented products. Secondly, the traditional FBS model was extended to construct an extended conceptual design model of "Demands-Functions-Behavior-Structure-Appearance". The process of model derivation was elaborated with emphasis on demand analysis and appearance coding. Then, the usability of the product was quantified by calculating the correct probability and reaction time of the elderly users to judge the function and operation mode of the product, so as to optimize the best design scheme of the elderly-oriented products. Finally, in the design application, the feasibility of NFBSA model was verified by taking the improved design of the usability of intelligent remote control of household electric nursing bed as an example. NFBSA model can effectively improve the usability of products, help to narrow the use gap between elderly users and elderly-oriented products, further enhance the confidence of elderly users in emerging products, and provide reference value for designers and related product usability design research.