Medium is a way to express idea and convey information. It’s the most important tool to spread information and exchange idea as well as conduct interpersonal communication in the human society. With the diversification of social culture and communicative content, the far-reaching development of media renders profound change to the ways of spreading information. Digital medium, as a new platform brought about by information digitalization, shares the same theoretical basis with traditional visual communication design with respect to design philosophy, and design elements. On the other hand digital medium shows distinctive aesthetic and formal feature in terms of modes of transmission and visual expression. This paper aims to discuss the design principle and theoretical basis of digital medium, to explore its relation with traditional visual communication design theory and thus to find out the theoretical evidence for the development of digital medium.