Abstract: Deep-sea oxygen isotope records reveal that the earth's climate has experienced times of gradual global coolings and ice sheets expansions at Antarctic and north hemisphere one after another. The mechanism for Cenozoic climate change from greenhouse to icehouse, however, still remain unclear. Various hypotheses related to declining atmospheric CO₂ concentration and models for changes in ocean circulation have been proposed to explain the Cenozoic global cooling, such as the BLAG hypothesis, plateau uplift-weathering hypothesis, uplift-organic carbon burial hypothesis, volcanic iron fertilization effect, island arc uplift-weathering hypothesis and passage opening and closing hypothesis. Base on the debates on the mechanism of Cenozoic climate cooling, this study reviewed the progress and defects of related researches in recent decades, and put forward some key points for future study, such as, establishing accurate evolution sequence of Cenozoic atmospheric CO₂ concentration, establishing a more accurate timetable of earth’s outgassing, Tibet plateau uplifting and passage opening and closing, establishing a solid weathering index system, reinforcing the study of volcanism and its oceanic biogeochemical effects on carbon cycles.