Abstract: The principle that “the present is the key to the past”, which has lead the geology acquired tremendous achievements, is and will continue to be the most important thought in the development of earth science．The problems on resources, environment and calamity that human society will face to in the 21 century are fundamentally the problems of geology. To be prepared for the new challenges, the geologists must change their way of thinking in geological research. If we recognize that evolution of the Earth in the history was in a way similar to that of today, the new principle that “the past is the key to the present and future” will become more and more important in the earth science. From the perspective of historical geology, study of the processes of geological events happened in the earth history, their evolutionary trends and environment impacts in the past and future, will be a major task of geology in the 21 century.