Bulk heterojunction polymer solar cells are promising alternatives to fossil energy for energy conversion. The synthesis of new materials, optimization of device structures, and interface engineering are feasible methods to improve the power conversion efficiency of polymer solar cells. In this study, research on interfacial engineering in polymer solar cells is reviewed from three aspects: interfacial materials, interfacial doping, and interfacial modification. Many experiments on interface modification have successfully promoted the generation and transport of carriers. It is proved that interface engineering is of great significance to improve the efficiency of charge extraction, passivate the surface defects, and enhance the conductivity.