Abstract: According to depositional characteristics and cause of formation of the sand bodies, the sandstones in Jiaxian-Zizhou area, Ordos basin can be divided into three types, they are the tidal-channel sandstone, channel sandstone and subtidal bar.The sandstones with different causes of formation have differ-
ences in such aspects as the texture components, the depositional structure, the well log as well as the sand shapes, which have apparent effect on late diagenesis types and strength, and in turn, they control the pores types, porosity and permeability of the reservoir. The study shows the tidal-channel sandstone plays the most favorable role in the reservoir formation and evo-
lution. Higher mature degree of the component and texture make stronger cementation. The dissolution and compaction are not obvious. All these make it possible that more grain pores and inter kaolinite crystal pores are kept and the sandstones have higher porosity and permeability. The second section of
Taiyuan Formation in the middle and south area will be important target in following exploration. The deposition of channel sands and subtidal sands determine that their accumulation property is poorer than tidal channel sands, and their distribution is restricted, they are composed of poor reservoir.

Key words: Taiyuan, sand body, cause of formation, diagenesis, reservoir