Recently, many people pay attention to design and construct various kinds of systems for digital city by means of automatic control, information and network technology as well as artificial intelligence in domestic cities and areas.

In this article, from system science point view, that a digital city is an Open Complex Giant System (OCGS) by the author is proposed. And the “ metasynthesis from qualitative opinion to quantitative understanding” which is the methodology of OCGS could be applied for dealing with digital city.