Abstract: The sector of organic solar cells (OSCs) is developing very rapidly. The charge-transfer (CT) states, formed at the interface between electron-donor (D) and electron-acceptor (A) materials, play a significant role in the photoelectric physical processes, such as exciton dissociation, charge separation and recombination. Since the introduction of the D-A mixed heterojunction in the active layer, the CT states have been focused by many experimental and theoretical research groups. Following the previous works, the characteristics of CT states were briefly summarized, and the impact on the properties of CT states and the processes of radiative and non-radiative recombination was descibed from morphology configuration, electronic polarization and delocalization at the D-A interface. In addition, the micro-mechanism of photoelectric conversion in the active layer and the challenges faced in the design of novel materials was outlined.