Clay mineralogical and mineral structural occupying analyses were applied to the clastic rocks and carbonates of Meso- Neoproterozoic in Jixian section, Tianjin, China. These analyses include illite crystallinity, chlorite crystallinity, clay mineral assemblages, particle size distribution, polytype, ordering degree, Mg/Ca ratio in dolomite structure and geothermo- geobarometer. The results demonstrate that illite crystallinity Kübler index ranges from 0. 37° to 1. 37° Δ2θ while chlorite crystallinity rkai index from 0. 31° to 2. 40°Δ2θ, gathering with 1Md polytype, uniformly indicating the late diagenetic stage encountered with these clastic rocks except two data falling in the incipient anchimetamorphic realm.The major clay mineral assemblages are illite, illite/smectite mixed- layer, chlorite/smectite mixed- layer phases and kaolinite, reflecting a certain paleo- environmental condition. The upper limit 24 nm of “Best mean particle size” from the range 8 to 24 nm well agrees with the size 23 nm of the anchizone/diagenetic zone boundary converted from NewMod with Kübler index 0. 42°Δ2θ. It also explains clearly the late diagenetic stage. The range of dolomite ordering degree is from 0. 19 to 0. 99. This range can be classified into four grades: very low- , low- , middle- and high- grade ordering zones. Compared with the situation of carbonates of Carboniferous- Permian in eastern Sichuan, the low- to middle- grade ordering zones have an appropriate prospecting for petroleum and gas. From the west to the east, dolomite ordering degree increases generally from 0. 19 to 0. 99. The estimated diagenetic conditions are 180 to 200±20℃ and 330 MPa pressure, and result in a paleo- geothermal gradient of 17~21℃/km.