Ultra wideband (UWB) wireless communication is a new type of radio communication. One of the main applications of UWB in the future focuses on wireless personal area networks (WPAN). Channel estimation is very important for OFDM based UWB system because of its coherent demodulation. In this paper, a new improved channel estimation method is proposed based on the characteristics of the practical indoor UWB multipath channels. Compared with the common estimator using discrete Fourier-transform, the proposed algorithm can properly choose suitable length of time-domain filter by distinguishing different channel conditions. It is shown by simulation that better performance can be achieved for UWB indoor channels