Abstract: The huge bandwidth of UWB signals inevitably incurs the interference with some existed narrowband systems within its bandwidth. In this paper, we proposed two novel modified non-linear chirp ultra wideband (UWB) waveforms to suppress narrowband interference (NBI). The two waveforms were designed based on the impulse radio UWB scheme. The energy of the two waveforms was distributed uniformly in time domain, which avoided the problem of high peak power. Both of them make no sacrifice to the useful signal, and they just required the simple processing in time domain but not the complex processing in frequency domain. Theoretical analysis and simulation results show that the NBI suppression ability of the direct-sequence binary phase-shift keying (DS-BPSK) UWB system with the two proposed chirp waveforms the conventional linear chirp based UWB system significantly.