Abundant unconventional natural gas resources have been found in coal measures deposited transitionalfacies in Carboniferous-Permian strata. In this paper, the author had carried out microscopic characteristics and physical simulation experiments on Shanxi Formation in Ordos basin, and found out that the main pore types of Shanxi formation includes organic matter pore, residual primary pore, unstable mineral dissolution pore and clay mineral interlayer pore. Interlayer pores of clay minerals and nano pores of organic matter are significant differences between shale and conventional sandstone reservoirs. Nano pores of organic matter are widely developed in coal measure strata of Shanxi formation. Through simulation experiments, it is believed that the forming processof nanopores is seriously related to the cracking gas of early formed liquid hydrocarbon in strata. With the asphaltation of crude oil, bubbles solidified in asphalt strips and converted nano pores. From Late Jurassic to the end of Early Cretaceous, abnormal thermal eventswhich controlled the generation intensity and scope of pyrolysis gas occurred widely in Ordos basin. Duringthe process of asphalting, lots of organic matter nanopores formed, which greatly improved the resource abundance of unconventional gas in coal measures. Thisknowledge from the experimentscouldtakea better understanding of the pore structure characteristics in coal measuresand be helpful for the selection of unconventional oil and gas prospecting area in Shanxi Formation.