Power allocation is a key issue for the application of relays in a communication system.With a proper power allocation strategy, the performance of the entire system can be improved and the overheads of relay would be reduced. However, in most cases, uniform power allocation (UPA) strategy is still widely utilized, which wastes the limited resources of the communication system and thus degrades the quality of service (QoS). Therefore, in this paper, we will compare optimal power allocation (OPA) strategy with UPA for the decode-and-forward (DF) relay station. Moreover, in this paper, the direct transmit link between the source and the destination will be considered. As a result of this consideration, a more convincible comparing result can be obtained. Finally, the better performance of OPA strategy over UPA strategy can be verified under a series of mathematical reasonings and simulations.