In this paper, a novel approach to interference mitigation with coexisting spectrum users for UWB pulse radio is proposed. This new approach uses adaptive frequency spectrum estimator to give the estimating values of each coexisting spectrum users' center frequency and band. Based on these estimating values, the frequency band of UWB communication system can be adaptively divided into multibands. The center frequency and the pulse shape of each sub-bands are also determined adaptively. This method successfully solves the coexistence problem between UWB systems and the existing systems, especially for stochastic existing users, without the need of reducing UWB pulse power spectral density (PSD) over the whole UWB frequency band. Therefore, the application range of UWB systems can be enlarged by increasing the transmitted UWB pulse power