A quality of service(QoS) guaranteed cross-layer resource allocation algorithm with physical layer, medium access control(MAC) layer and call admission control(CAC) considered simultaneously is proposed for the full IP orthogonal frequency division multiple access(OFDMA) communication system, which can ensure the quality of multimedia services in full IP networks.The algorithm converts the physical layer resources such as subcarriers, transmission power, and the QoS metrics into equivalent bandwidth which can be distributed by the base station in all three layers. By this means, the QoS requirements in terms of bit error rate(BER), transmission delay and dropping probability can be guaranteed by the cross-layer optimal equivalent bandwidth allocation. The numerical results show that the proposed algorithm has higher spectrum efficiency compared to the existing systems.