Multiple antennas technique which is introduced into UWB system is an effective method to improve transmission quality, enhance the system performance and decrease the bit error rates (BER). However, the large number of antennas requires lots of expensive hardware. Combining antennas selection and power optimization technique can decrease hardware cost and complexity, and enhance the system performance. In the case of knowing entire channel state information (CSI), in this paper, maximum ratio transmission (MRT) and transmit antennas selection (TAS) technique are introduced at the transmitter. Based on the maximal channel power gain which is adopted as an antennas selection criteria, the better antenna subset (MT,2;MR) is always operated on the system, and then the selected double antennas transmit power are allocated by the MRT technique. Simulation results show that the bit error rate (BER) of the UWB system obtain obvious improvement after combining MRT with TAS.