The Middle Miocene Climate Transition (MMCT, 14.2~13.9 Ma) was a global climate change event characterized by significant changes in ice sheets, ocean currents, and carbon cycles. Clarifying the driving mechanism is important for understanding the global cooling during the Cenozoic. Two hypotheses have been proposed to explain the mechanism of MMCT, one emphasizing the reorganization of ocean circulation and the other highlighting the importance of the carbon cycle. However, neither hypothesis can explain the various phenomena of the MMCT. The ice sheets, ocean circulation, and carbon cycle are crucial in the mechanism of the MMCT, and form a coupled system that causes climate change on Earth. With the help of these three elements and combined with geological records, these two mechanisms lead to an increase in deep ocean carbon storage and a decrease in atmospheric pCO₂, which further promotes climate cooling and ice sheet growth. In comparison with that on carbon cycle processes and ice sheet changes, existing research regarding ocean circulation, particularly in the deep Southern Ocean and Pacific Ocean, during the MMCT period is insufficient. Consequently, future research should focus on the changes in ocean circulation in these key regions to improve our understanding of the forcing mechanism of MMCT.