Abstract: By systematically studying three assemblages of the Yima Formation flora of Western Henan Provinec situated in southern border of North China Platform,and taking the dynamic changes of fossil plant assemblages and the foliar physiognomy of fossil plants as the evidences,authors conclude that the climate in the research area began to get hot from the Bajocian to the Early Bathonian during the Middle-Late Jurassic,which is obviously earlier than that South Europe,Middle Asia and Siberia regions did.