AN style="FONT-FAMILY: ’Times New Roman’,’serif’; FONT-SIZE: 10.5pt; mso-font-kerning: 1.0pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA" lang=EN-US>The reservoir rocks in Shangsi Formation of Lower Carboniferous in Jiadaozhai of South Guizhou sag are marlstones and crystal powder dolomites, followed by bioclast limestones and dolomitic limestones. Based on the slice observation and physical properties of the reservoir in Shangsi Formation, this paper indicates that the main reservoir spaces are fractures, followed by intergranular (intragranular) dissolved pores and intercrystalline (dissolved) pores. It is a fractured-porous reservoir with low porosity and low permeability. The development of the reservoir is determined by diagenesis. The cementation, compaction and recrystallization have destroied most original pores, and late-stage dolomitization, dissolution and tectonic disruption have formed many secondary pores and fractures.