This paper suggests oxygen isotopic composition of horse teeth as a new substitute climatic signal.Based on the oxygen isotopic composition of modern horse(genus Equus)tooth’s enamel which collected from different places in the world,it setst up a linear equation between the oxygen isotopic composition and annual average temperatures:δ(18)O=0. 5080T+10.49(r=0.82). It proves that oxygen isotopic composition of horse teeth responds to that of precipitation,and represents the average value in a ecological region. Because mammal tooth’s enamel is able to efficiently resist influence of diagenesis,oxygen isotopic composition of fossil horse teeth can be used to estimate annual average temperatures in geological time,especially to provide quantitative analytic materials for changes of climate and environments in the Quaternary.