In recent decades, the demand for clean and renewable energy has grown increasingly urgent due to the irreversible alteration of the global climate. As a result, efficient organic solar cells (OSCs) have gradually gained attention as a study hotspot. To break up this dilemma, this paper reviews the molecular design strategies of benzodithiophen (BDT)-based polymer and small molecule donor materials since their birth, focusing on the development of main-chain engineering, side-chain engineering and other unique molecular design paths. Up to now, the state-of-the-art power conversion efficiency (PCE) of binary OSCs prepared by BDT-based donor materials has approached 20%. Our work detailly discusses the potential relationship between the molecular changes of donor materials and photoelectric performance in corresponding OSC devices, thereby presenting a rational molecular design guidance for stable and efficient donor materials in future.