This paper discussed the definition, geographical tradition and technology driven development mechanism of geographical information science, and came to a conclusion that geographical information science is a new paradigm of geography after information revolution, then put forward the theory framework of this new subject. Classical geography is focused on describing the pattern of geographical objects on epigeosphere by field surveying mainly, so it is essentially an information science. With computer and information technology introduced, geographical science system is being reconstructed, and there are three main development directions: one is regional economic research, which emphasizes relations between different benefit groups; one is ecological or environmental research, which emphasizes transference and transformation of material and energy; and the other is geographical information research. The first two directions are about material flow、energy flow and human flow of geographical system, however the last one is focus on information flow, and tries to describe and analogize epigeosphere information transformation mechanism by use of modern information technology. So geographical information science succeeds and resembles classical geography in methodology and theoretics, and is a new paradigm of classical geography. Geographical information science system includes theoretical、technical and applied geographical information science. Its development is dependent on the combination of geographical information researchers and classical geographers.