Abstract: Mesozoic era is a crucial stage for the Earth development and life evolution, and is particularly significant for bearing typical greenhouse climate that is the closest to today. Among them, the Cretaceous is considered as one of the best example of the greenhouse climate in Earth history. Recent progresses including fossil plant stomata parameters, paleosol isotope and geochemical model, made it possible to synthesize the CO2 variations throughout the Cretaceous. The results showed that atmospheric CO₂ levels remained relatively high throughout the Cretaceous, but they were lower in the early Cretaceous, highest in the mid-Cretaceous and gradually declined during the late Cretaceous. However, this overall trend was interrupted by several rapid changes of paleo-CO₂ associated with some geological events. It thus showed that the Cretaceous greenhouse climate condition is not as stable as we thought before, but instead with some short-term fluctuations related to the brief episodes of climate change.