The performance of bulk heterojunction organic solar cells based upon blends of donor and acceptor materials has been shown to be highly dependent on the microstructure and photoelectric properties of active layer. Recently, various methods, such as post-annealing, microwave annealing and control in the film-forming rate, and so on, have been used to modify the morphology to achieve high device performance. Among these methods, adding additives is a simple and promising approach, which can not only control the morphology but also improve the photon absorption or energy-level distribution of the active layer. In this review, we will introduce the additives that used widely in recent from following aspects: species, mechanism, and performance. First, the additive species and its selection principle according to special donor and acceptor system will be concluded. Then, the mechanisms of improved morphology and photoelectric properties by adding different kinds of additives will be illustrated in brief. At last, we will discuss the influences of additives on device performance.