Pore structures are significant for evaluating shale gas production since they not only control gas capacity but also affect hydraulic fracturing. In this study, we investigated the pore structures of Longmaxi (LMX) shale samples from a shallow drill core in Guizhou Province, China, with large-area electron imaging and neutron scattering. Pores related to the mineral matrix and organic matter (OM) were identified, and the former had greater impacts on the pore shape and porosity, which would enhance fracturing. Large-area electron imaging analysis (with 15 nm resolution) indicated that the majority of LMX shale porosity was contributed by nanopores with diameters smaller than 400 nm. According to the neutron scattering data, micropores and mesopores dominated the pore size distribution (PSD), and pores within cross sections cut perpendicular to the bedding showed preferential orientation accompanied by larger porosity. The porosity (4.6-5.6%) calculated from neutron scattering data was approximately 2 times larger than that calculated from imaging data, suggesting that nanopores smaller than 15 nm contributed more to the porosity than those larger than 100 nm, as they were more resistant to compaction. This study indicated that pore types were controlled by minerals as well as thermal maturity, while PSDs were affected by tectonic movements. The majority of porosity originated from micropores and mesopores, which confirmed the great potential for shale gas reserves in the LMX shale. This conclusion is helpful for building a shale porosity model and eventually improving the reserve assessment.