The pore structure of shale reservoirs controls the enrichment and migration of shale gas and the organic matter (OM) pores are an important gas storage space. As the pore structure characteristics of different components of organic matter are still unclear, relevant research is urgently needed. This study takes the Longmaxi Formation shales of the Changning, Luzhou and Yuxi blocks in the southern Sichuan Basin as the research objects, and divides Longmaxi Formation shale samples into different lithofacies based on organic geochemical and mineral composition analyses. Field emission-scanning electron microscopy (FESEM),in combination with image-processing software, is used for quantitative characterization of OM pore structure within theshale samples. The pore structure parameters of shale samples with different lithofacies from different blocks are obtained by N₂ adsorption and high pressure mercury intrusion porosimetry experiments. The results show that OM with different pore structure characteristics can be divided into Type A, Type B, Type C, Type D and Type E. The difference of organic macerals, mineral composition and abnormal pressure lead to the distinctive OM pore structure parameters such as pore diameter, area porosity and morphology. The differential development of OM pores is an important factor causing different reservoir spaces for different shales. The reservoir space of shale samples in the Changning block dominated by Type B and Type D OMs is the most developed,followed by shale samples in the Luzhou block dominated by Types A, B and D, and the reservoir space of shale samples in the Yuxi block dominated by Types B and C is the least developed. The outcomes of this work are significant for improving shale reservoir evaluation and selecting optimal shale lithofacies.