Polymer photovoltaic cells with organic polymer materials as the active layers for an increasing power conversion efficiency have become a research hotspot in the field of photovoltaic devices in recent years. In this paper, Internal mechanism of polymer/fullerene solar cells are elaborated exhaustively, including light absorption, exciton diffusion and dissociation and charge carrier transport as well as extraction. Furthermore, the optimization of device structure, morphology control and interface modification are introduced to improve performance of polymer/fullerene solar cells. Power conversion efficiency and the various structures which can be achieved are discussed in detail. The future prospects of polymer photovoltaic cells are also expected.