In this paper, the propagation characteristics of UWB (Ultra-wideband) signal in the indoor NLOS (Non-Line-of-Sight) environment are discussed based on the time-domain ray tracing method. Propagation characteristics are analyzed by considering of multipath propagation mechanisms including direct ray, reflection and transmission, such as the time-domain normalized electric field intensity, instantaneous power delay profile, received power and so on. These results provide the theoretical basis for wireless communication network coverage and optimization of UWB signal in the complex environment of indoor.