Ultra-wide bandwidth (UWB) is a prospective radio technology for wireless networks. As being approval by FCC, UWB radio has received much attention. In this paper, we propose a new multiple access protocol for time-hopping UWB ad-hoc network. As UWB system is a carrier-less impulse radio system, it is cumbersome to implement the carrier sensing capability needed in popular approaches such as carrier-sense, multiple access with collision avoidance (CSMA/CA) MAC protocols. The novel multiple access scheme to detect the busy medium and reduce the probability of collisions in TH UWB ad-hoc network is given out and evaluated. In UWB TH modulation, the spreading codes for target node are used. In our scheme, another binary PN sequence according to the destination node is also added to the modulation scheme to sense the busy medium before transmission. Communications outside the definition of directly transmission region (DTR) have to relay over intermediate nodes.