Abstract: Geomicrobiology is a new branch of earth sciences developed since the end of the twentieth century. It studies mainly the microbial processes in geologic environment and all kinds of geochemical records generated in these processes．Through microbial existence and evolution in the earth history at the various extreme environments such as high temperature，high pressure, extreme acidity and alkalinity，high salinity, very high radioactivity，large earth depth，etc．and different kinds of geochemical records in the interactions between microorganisms and their geologic environments，this discipline studies the cycling of life-essential elements(C，H，O，N，S， Fe, etc．)in the global and local scales in relation to microorganisms in the Earth’s history to set a context for further research for the microbic weathering， biomineralization，microbic ecocycling in the geologic environment and the eco1ogical environment．The present paper also concerns the interaction of microorganisms with minera1s, microbic ecology at the extreme environments，and molecular geomicrobiology．