The paper proposes a clustered dynamic source routing (CDSR) protocol based on the hierarchical topological infrastructure in view of the lack of extension of flat unicast routing protocols in large-scale Ad Hoc networks. CDSR protocol adopts the advantages of on demand and source routing in DSR (dynamic source routing), and introduces enhanced weighted clustering algorithm (EWCA) to assure the stable hierarchical topological structure to manage hierarchically network hosts. The simulation experiment proves the protocol has the advantages of low delay, high delivery ratio and good extension, and proves the protocol better suitable for large scale Ad hoc networks.