Sandstone reservoir in the Upper Paleozoic coalbearing strata of the Ordos basin is generally characterized by low feldspar content and welldeveloped dissolution pores. Combining with structure background of the Ordos basin and the thermal evolution history, we studied mechanism from which a large amount of feldspar disappeared in Upper Paleozoic coalbearing strata using thin section identification, Xray diffraction, scanning electron microscopy (SEM), geological conditions (high temperature and high pressure) of sandstone acid dissolution experiment. It can be concluded that pickling effect of the abnormal heat during Early Cretaceous resulted in disappearance of large volume of feldspar in the Upper Paleozoic coalbearing strata, giving a rise to the formation of widely distributed secondary dissolution pores. The distribution of feldspar has nothing to do with buried depth, and difference of thermal evolution degree controlled directly the disappearance of feldspar. Based on the research above, this study established the model of diagenetic evolution of the Upper Paleozoic coalbearing strata and secondary solution pore development in the Ordos Basin after completion of feldspar dissolution.