Abstract: The tooth enamel of mammalian fossil is able to be efficiently resistant to diagenesis and retains the original carbon and oxygen isotopic composition. On the basis of the analyses to the isotopic composition of herbivorous mammalian tooth enamel, the paleoclimates when these mammals. lived can be reconstructed. The carbon isotopic composition of structural carbonate in tooth enamel responds to that of dietary plants. According to this principle, the proportions of C3 and C4 plants in the terrestrial ecosystem can be estimated, which were controlled mainly by C02 atmospheric levels, moisture stress and irradiance as well as related to different latitudinal or climatic zones. The oxygen isotopic composition of biogenic phosphate in tooth enamel responds to that of ingested water from precipitation whose oxygen isotopic composition responds to temperature variations. As a result, there is an outstanding correlation between oxygen isotopic composition of tooth enamel and temperature. In the light of this pattern, the annual average temperature in the geological periods can be calculated and the climatic variation curve of cold and warn-I in the geological periods can be made.