In Flying Ad-hoc Networks (FANETs), frequency resources are scarce, and factors such as node mobility, Multi-Beam Directional Antennas (MBDAs) directionality, and co-frequency interference bring impacts on achieving reliable communications. In this paper, an efficient frequency resource allocation method based on beam frequency reuse is proposed to ensure the adaptation to topology changes and solve the problem of rationally allocating limited frequency resources among multiple nodes. Simulation results show that the proposed frequency allocation method, under the priority mechanism based on spatial isolation angle and reuse frequencies, achieves distributed decision-making among nodes by coordinating frequency allocation to avoid co-frequency directional beam interference. This method addresses the common frequency band matching issue between the transceiver nodes, ensuring stability and communication quality, and contributing to the reduction of interference among co-frequency links.