Silver nanoprisms (AgNPs) affect the performance of organic solar cells (OSCs) in different ways depending on their positions in the device. To investigate this issue, we incorporate AgNPs in different positions of OSCs and compare their performance. The power conversion efficiency (PCE) is improved by 23.60% to 3.98% when the AgNPs are incorporated in front of the active layer. On the other hand, when AgNPs are incorporated in the back of the active layer, the short-circuit current density (J_SC) is improved by 17.44% to 10.84 mA/cm². However, if AgNPs are incorporated in the active layer, both open-circuit voltage (V_OC) and JSC are decreased. We discuss the position effect on the device performance, clarify the absorption shadow and exciton recombination caused by AgNPs, and finally indicate that the optimal position of plasmonic AgNPs is in front of the active layer.