Clay minerals have such main types as illite, chlorite, smectite and kaolinite. They could record rich information of climatic and environmental changes during their formation and hence are good proxies in climatic and environmental study. Many factors such as tectonic movement, climate, basin size, surface parent rocks, soils, vegetative cover, landscape, water media properties, wind and diagenesis, affect the clay mineral formation. The types and quantity of clay minerals in strata depend on these factors in varying degrees. Tectonic movement and climate are two primary factors which dominate the types and quantity and control other secondary factors which influence clay mineral formation. It is very difficult and unsuitable to analyze climatic and environmental changes during the tectonic movement phase only by clay minerals. For a long geological time which has tectonic movement, sedimentary facies and palaeogeography must be used to decipher paleogeography and plaeo-environment information. However, under stable tectonic movement, which spans usually a short geological time, other information factors keep stable and clay minerals are formed mainly through climatic factors. They record the real information of climate and environment changes and hence can be used as climatic proxies. Basin change of climate and environment could be inverted. So, climate is the key factor for forming clay minerals and determining their amounts. Strata-tectonic analysis must be done when clay minerals are used to decipher climatic and environmental information. In a word, when tectonic movement is stable, climate becomes the dominate factor affecting clay mineral formation. The other secondary factors keep invariant and clay minerals carry the major climatic information，and they can be used to decipher climatic and environmental history. The mixture of clay minerals caused by ground hydrographic systems affects the signal clearness of clay minerals carrying major climatic information and environments. Sedimentary-buried diagenesis of clay minerals in strata shouldn't be ignored in analysis.