Hybrid routing protocol combines proactive with reactive techniques, with the advantages of high reliability and low routing overhead. The Zone Routing Protocol (ZRP) is a typical hybrid routing protocol. This paper presents an improved ZRP routing protocol based on cluster domain mechanism. This protocol replaces partition in ZRP routing protocol with clusters in hierarchical network, and proposes a new domain routing method to avoid redundant or duplicate route requests. Theory analysis and simulations show that the ETE delay, routing overhead and packet delivery ratio performance of the protocol proposed here are superior compared to the traditional ZRP protocol.