Atmospheric CO2 concentration is closely related to the climatic change of the Earth greenhouse. A stomatal parameter of fossil plants has been proved as an effective biological indicator of reconstructing paleo CO2. Well preserved fossil specimens of Baiera furcata were collected from the Lower Jurassic Daxigou Formation of the Agan Town, the Middle Jurassic Yaojie Formation of the Lanzhou City, Gansu Province and the Lower Cretaceous Huolinhe Formation of the Huolinhe Basin, Inner Mongolia. The epidermal characteristics of the present specimens were analyzed, and the stomatal parameters were calculated. According to the stomatal parameters of Baiera furcata and the nearest living relative specie Ginkgo biloba, the paleo CO2 of the late Early Jurassic, the early and middle Middle Jurassic and the early Early Crecateous were quantitatively reconstructed at about (1263±71)×10-6、(1388±24)×10-6、(1599±31)×10-6 and (1899±198)×10-6. This result coincides with the CO2 curve of global carbon balance model (GEOCARB I—Ⅲ), which indicates that B. furcata is a good biological indicator for reconstructing the paleo CO2. Combining with the result of the Mesozoic paleo CO2 values obtained by other terrestrial plants, it is found that all the estimated values are lower than the values of GEOCARB I—Ⅲ. It can be deduced that the terrestrial atmospheric CO2 concentration was lower than the marine CO2 level in the Mesozoic. In addition, stomatal cluster can be found on the lower epidermis of B. furcata, which was the result of adaption to the environment.