In this paper,first,the problem of resource allocation of relay OFDMA systems is described as a mathematical model with power-limited access nodes and maximum system capacity,which meets the requirements of miminum rate of each user.Then,a resource allocation algorithm based on dual decomposition is proposed,which decomposes the problem into several subproblems of subcarriers,thus effectively recuding the calculation complexity.By solving the subproblems,optimal schemes of relay node selection,power allocation and subcarrier assignment can be obtained.Simulated results show that the proposed algorithm effectively improves the system capacity and simultaneously meets the rate requiremnets of each user.