How to efficiently use the spectrum resource to provide quality-of-service (QoS) support is a challenging task for wireless communication systems. In this paper, a resource reservationbased on-demand spectrum assignment and routing protocol is proposed to provide QoS support for IEEE 802.11-based multiradio multi-channel ad-hoc networks. Our work distinguishes from prior ones in that we don't treat the spectrum as the set of discrete orthogonal channels but the continuous resource, i.e. we use channel width adaptation when allocating spectrum resource. We develop distributed resource assignment protocols that utilize the AODV routing to perform admission control and resource reservation. Simulation results show that our protocol can efficiently utilize the network resources to provide QoS support.