Four clay minerals of the middle and late Meesozoic mudrock samples from North and Northeast China were analyzed by TEM and Illite Crystallinity (IC) in the study. The paper also explained the reliability of experimental data when employed to analyze paleoclimate. Spatial and temporal change of contents of clay minerals, features and evolution of paleoclimate, as well as the relation between the change and paleohighland, were also discussed in the research. The result shows that illite is the most common clay mineral in the study area during the Middle and Late Mesozoic. The contents in each study area is no less than 20% (averaging to 46.6%). The content of smectite ranks the second with an average of 57.8% in Henan and Shandong provinces. Both kaolinite and chlorite are less common in most the study area, but relatively abundant in Shanxi province, indicating that the studied area was dry and cold during middle and later Mesozoic time, except that climate in Shanxi changed between dry cold and humid. This, to some extent, demonstrate ancient highland was there, i.e., the "East China Paleo Plateau". However, there are some differences in both time duration and space distribution between the the "highland" and "plateau" although it is temporally cited as "plateau". Herein the "Eastern China paleo Plateau" is defined as a highland developed from Middle Jurassic through Cretaceous (even to the end of the Paleogene) in North and southeastern and Northeast China. It is confined in Shanxi, Henan and Shandong provinces in early stage (Middle Jurassic) and spreaded to eastern Liaoning province in middle late stage (Late Jurassic and Cretaceous). It is proposed that the plateau had not influenced all the Northeast China during the time, and could alter the climate in northern Hebei and western Liaoning in Late Jurassic and Late Cretaceous. In addition, it is also suggested that the matter in the plateau could be transported into the paleo Pacific ocean by two outlets at the end of the Tanlu strike slip fault in Middle Jurassic and Early Cretaceous, and most of the plateau could be eroded and transported into sedimentary basins around the highland.