Abstract: Although A'nan depression has been well prospected in past years, no lithologic reservoir has been discovered. The special lithologic section of the Tengger Formation is the potential reservoir strata. Based on lithologic characterization, scanning electronic microscopy, and electron probe measurement, the authors investigated the reservoir properties of the special lithologic section. The lithologic section is mainly composed of gray dolomitic mudstone, argillaceous dolomite, calcareous sedimentary stuff and calcareous fine sandstone intercalated with gray green massive tuff. The calcareous cementation and clayey cementation are the main types of ce-mentation. The tuff and sedimentary tuff elemental geochemical analysis shows that, with the alteration of diagenesis fluid, the silicate and sedimentary tuff dissolved significantly, which led to abundant secondary pores and strong depletion of heavy rare earth elements. These secondary pores and intergranular pores together with micro-fracture constitute the main potential reservoir space and the migration paths of the hydrocarbon.