Abstract: The paper analyses distribution of Cretaceous clay mineral and its sedimentary and diagenetic significance in Ordos basin. The clay mineral components of the Cretaceous sandstone and mudstone samples are dominated by illite, chlorite and illite/smectite mixed layers in Ordos basin. The clay minerals of mudstones are mainly from siliciclastic deposits, and a small amount is authigenic mineral assemblage formed during depositon and diagenesis, however the clay minerals of sandstones are both from siliciclastic deposits and authigenic mineral assemblage in diagenesis. The clay components and distribution of the sandstones and mudstones show that Ordos basin has totally experienced arid-semiarid climate during the Cretaceous but occasionally humid climate, and the Cretaceous deposits have rich silicate minerals such as feldspar, and the sediments are sourced mainly from the northern, southern and western margins of the Ordos basin. The salinity of sedimentary and diagenetic water bodies both are high, and are rich in K+、Fe2+、Mg2+. It generally shows that the salinity is higher in the south than in the north and the K+、Fe2+、Mg2+ contents are richer in the south than in the north.