[Methods]Plant fossils are the best materials to record terrestrial climate change in geological history, especially to the change of the paleo-CO2 concentration. Phoenicopsis (Windwardia) cf. rudinervis was identified due to the study of the morphology of the fossils collected from the Jurassic Yan ''an Formation in well Ningdong 2, Yanchi area, Ordos Basin. [Objective]In order to reconstruct the paleo‐atmospheric CO2 concentration, paleo‐temperature and water use efficiency of plants during the Middle Jurassic, leaf fossils of Phoenicopsis (Windwardia) cf. rudinervis were selected from horizon for calculating the the epidermal stomatal parameters and their isotope carbon composition of leaf cuticles. [Results]The results show that the average stomatal index (SI) of Phoenicopsis (Windwardia) cf. rudinervis is 4.25%, The paleo‐atmospheric CO2 concentration obtained by the stomatal ratio method is 1599 ppm. The paleo‐average temperature of Yanchi is about 1.2℃~31.4℃. The average value of the stable carbon isotope δ13C of plant fossils is -23.6‰, and its water use efficiency (WUE) is calculated to be 348.2 mmol/mol. [Conclusions] In general, the Middle Jurassic of Yanchi area in Ordos Basin belongs to a warm temperate - subtropical humid climate which reflected by the high CO2 concentration. Compared with previous data, we speculate that the paleo-CO2 concentration of the Middle Jurassic in northern China was significantly higher than that of the Early Jurassic, which may be related to the large-scale volcanic activities of the Yanshan Movement.