As the result of its special structural feature and depositional setting, Ordos Basin formed large scale low-permeability reservoir. According to scanning electron microscope, casting sheet image, core observation, physical property analysis and core analysis testing, this paper summarized and analyzed ultra low permeability reservoir microscopic feature of Ordos Basin Baibao area Chang63. Reservoir microscopic feature is controlled by deposition and diagenesis. Deposition decided reservoir lithology, interstitial content and sizes of primary pores. Compaction and cementation of diagenesis destroyed primary pores, but denudation provided high range secondary pores, which improved storage space of the research area.