In this study, we incorporated gold nanoparticles (Au NPs) in the Cs2CO3 buffer layer. Au NPs induced the effect of localized surface plasmon resonance (LSPR) in organic solar cells and improved the device performances. We found the short-circuit current density (Jsc), fill factor and power conversion efficiency (PCE) were obviously improved, while the open voltage( Voc) remained unchanged after doped the Au NPs. As a result, the PCE of the device incorporating Au NPs improved to 3.54% from the value of 3.12% for the device fabricated without Au NPs. Furthermore, we calculated the rate of exciton generation and the probability of exciton dissociation; they were both enhanced after doping Au NPs. It was proved that LSPR could not only enhance light absorption but reduce the recombination of electron-hole pairs in the active layer thus increasing the photocurrents and fill factors.