Abstract: There are various types of secondary porosity in Taiyuan sandstone at Shuangshan region, Ordos basin.Based on the observation of drilling cores and measurement of identification of casting thin sections under microscope, the paper discusses the mechanism of secondary porosity, so as to guide the exploration of natural gas. The mechanism of secondary porosity in Taiyuan sandstone was discussed from four factors including corroded material foundation. acidic and alkalic fluid dissolution, infilling of authigenic minerals and tectonic fracture, the acidic dissolution and infilling of authigenic minerals play a leading role in the area.