Abstract: The shale of Lower Silurian Longmaxi Formation in Changning area of Sichuan Basin is studied for its petrologic characteristics, mineral compositions, types and influencing factors of reservoir space, on the basis of field survey of outcrop profile, along with SEM and mineral content analysis. The results show that four kinds of reservoir space, including pyrite pore, intergranular micropore and microcrack in clay minerals, organic matter pore and interlayer bedding joint are developed in the shale, which are controlled by lithofacies, mineral composition and diagenesis. The obvious mineral characteristics of shale reservoir are of great significance for the exploitation of shale gas in the study area.