Abstract: As a hot topic in the field of complex networks, the problem of Internet validity is studied. General definitions of Internet space validity and time validity are given, then their physical characteristic parameters, i.e., networks density and Internet traveling diameter, are formally defined with quantitative analysis. Based on the mathematical relationship between the two parameters, which is derived from a series of known formulae, the definition of Internet validity factor is put forward as a parameter to connect Internet space validity with time validity so as to judge comprehensively the Internet validity. A mathematical model of validity factor based on time-evolvement analysis is thus given, which makes it possible to forecast and estimate the development of Internet in the future.