Abstract: The influence of carrier frequency offset (CFO) and sampling frequency offset (SFO) on the system performance in multi-band orthogonal frequency division multiplexing ultra wideband (MB-OFDM UWB) system and frequency synchronization was analyzed. First, preambles were used to estimate the CFO in time domain, the estimated value was averaged according to each frequency band's SNR in order to improve the estimate precision. Second, pilots were used to estimate the residual CFO and the SFO in frequency domain. In the end, the residual phase error was compensated in frequency domain. Analysis results show that, the methods are suitable for each band group (BG1~BG5) and all frequency hopping patterns (TFC1~TFC10). The simulation results show that, when SNR is 15 dB, the mean square error level of normalized CFO is 10<sup<-16</sup<, the mean square error level of normalized SFO is 10<sup<-10</sup<. The design method is of high accuracy, and is suitable for high speed MB-OFDM UWB system.