To ensure the effectiveness and reliability of a broadband power line communication network, an Orthogonal Frequency Division Multiplexing (OFDM) cross layer resource allocation method is proposed. It integrates the information of the service, network, Media Access Control (MAC) and physical layers of a multi-hop relay broadband power line communication network. First, the utility value model of packet scheduling in the MAC layer and the subcarrier allocation model in the physical layer, based on fairness threshold control, are established. A priority scheduling criterion of packets with higher efficiency value in the MAC layer is proposed to meet the service quality requirements of each user. Then, the model and criteria are applied to the resource allocation of cross-nodes in broadband power line communication networks. Finally, the proposed and comparison algorithms are simulated in a typical power line channel environment. Simulation results show that the proposed algorithm can meet the service quality requirements of real-time users and non-real-time users in terms of communication rate and delay. It has larger system throughput and better delay characteristics. Thus the OFDM resource allocation problem in a multi-hop relay broadband power line communication network is solved in an effective manner. This work is supported by the Natural Science Foundation of Hebei Province (No. E2019502186) and the Science and Technology Planning Project of Hebei Province (No. 17211704D).