To ascertain the contribution of different pores to shale gas reservoir, pore types, size and distribution of Lower Paleozoic marine shale in southern Sichuan Basin were studied using a variety of analytical testing methods. Pore space characteristics and influencing factors were discussed. The results show that Lower Paleozoic shale reservoir space can be divided into three main types, including mineral matrix pores, organic pores and micro-fractures, and can be further subdivided into nine types. Organic pores and interlayer pores between clay minerals are mainly developed in Longmaxi shale. Organic pores, dissolution pores and fractures are mainly developed in Wufeng shale. Organic pores are rarely in Jiulaodong shale, where dissolution pores and fractures are well distributed. Pore types and distributions show differences in Lower Paleozoic shales, which are mainly affected by mineral composition, the abundance of organic matter and diagenetic evolution. Micro-pores are developed in Lower Longmaxi shale, with high specific surface area, providing a bulk of reservoir spaces for shale gas adsorption, which makes it a beneficial shale reservoir.