Abstract: To solve the inter-cell interference problem in ultra-dense networks (UDN), a distributed interference coordination method based on network duality is proposed. Firstly, a new TDD frame format was designed, and the channel estimation stage and the iterative stage were added to the original frame format of LTE standards. Then due to the network duality, a new iterative interference coordination algorithm to maximize the network sum-rate was designed, combining the optimization goal of maximizing the signal to interference noise ratio (SINR) and the optimization goal of minimizing the residual interference. Theoretical analysis and simulation results show that good performance can be got after the first iteration, when the iterative initial value is set based on the maximizing signal to leak interference and noise ratio principle. And the method can complete in a relatively short period of time, need only local channel information, implement easily in the UDN, and outperform other distributed iterative interference coordination algorithms.