In order to improve the performance of the Ultra-Wideband(UWB) under the situation of low signal and noise ratio，by using the UWB indoor channel model proposed by IEEE 802.15.3a study group，the performance improvement of the binary pulse position modulation Time Hopping Ultra-Wideband (2PPM-TH UWB) systems is analyzed in the case of employing multiple receive antennas. Under ideal power control, the diversity performance of 2PPM-TH-UWB systems is evaluated for different numbers of antenna elements and selected multipaths. The simulation results indicate that the system property becomes better as the number of antenna elements and Rake fingers increases, and the effects of the spatial diversity upon improving system performance are better than that of the temporal diversity.