Quality-of-Service (QoS) aware scheduling in cooperative orthogonal frequency division multiple access (OFDMA) systems has long been a critical yet challenging research topic for achieving full system utilization. The optimal performance of such systems can only be achieved by joint optimization of various resources (power, bandwidth and etc). In this paper, we investigate the optimization of base station power allocation with QoS requirements in cooperative OFDMA systems. We formulate the QoS aware resource allocation problem and exploit its structure to derive an efficient solution. By employing Lagrangian relaxation, the problem decouples on each subcarrier into a hierarchy of subproblems. Combined with an iterative procedure, some separable and parallel structures could be exploited to obtain an efficient solution. Simulation results demonstrate that our proposed method outperforms previous works in terms of spectrum efficiency and QoS satisfaction.