In ultra dense networks, full-frequency multiplexing can improve the throughput of the network,but lead to serious inter-base station interference. In order to reduce the inter-base station interference,this paper firstly describes the interference degree between the small base stations by interfering with the weight value, and establishes a reasonable interference map. Then the clustering problem is transformed into Max k-cut problem, and the small substation is clustered by the improved suboptimal heuristic algorithm. Finally, the sub-channel is assigned to the users in each cluster by the channel assignment algorithm. The simulation results show that the interference management scheme can improve the spectral efficiency and average throughput of the system while reducing the interference between the small base stations.