Maceral is the organic petrology element of organic matter (OM) composition in shales. The origin and evolution characteristics of macerals in shales not only determine the hydrocarbon generation potential of shales, but also affect the formation and development of organic pores in shale reservoirs. On the basis of systematically summarizing the classification, origin and evolution characteristics of the maceral components in shales, this paper analyzed the effects of the evolution of different macerals on the development of organic pores. Macerals in shales can be classified into five maceral groups: liptinite, vitrinite, inertinite, zooclasts, and secondary organic matter. Different macerals have different generation potential and different thermal evolution properties, which lead to differences in development of organic pores. The oil-generating macerals, represented by algae, have a high hydrocarbon generation conversion rate and can provide excellent conditions for the development of organic pores. With increasing maturity, the solid bitumen and crude oil generated during hydrocarbon generation can generate more secondary organic pores by cracking. The hydrogen-poor macerals, such as vitrinite and inertinite, have only primary organic pores, and can not develop secondary organic pores.