Abstract: Aiming at the problem of serious inter-layer interference caused by dense deployment of base stations in ultra-dense networks (UDN), a model of maximizing the total system throughput considering spectrum reuse and co-channel interference is constructed, and a joint spectrum resource optimization method based on block coordinate descent (BCD) method (called JROBB) is proposed. The original problem is decomposed into three sub-problems: clustering, sub-channel allocation and power allocation. The sub-channel allocation and power allocation are iteratively optimized by the block coordinate descent method to approach the optimal solution of the original problem. Simulation results show that the system total throughput is improved by at least 22% on average compared with the existing typical algorithms, and the spectrum utilization can be effectively improved.