In order to scale up the wireless sensor network scope and achieve satisfying network performances, a new protocol called RBPC (RREP Broadcast with Passive Clustering) is proposed in this paper. By means of broadcasting RREP (Route Reply) packets with expanding ring, a large part of data sources do not have to initiate the route search and substantial routing overhead is saved. In the mean time the technique of expanding ring refrains unnecessary RREP packets from ongoing spread, and thus reduces the overhead to a large extent. Furthermore, some modifications based PC (Passive Clustering), like distance determined deferred time and power adjustment, are also proposed in this paper. Performance analysis has been obtained via simulations. It is shown that RBPC outperforms AODV/PC in reducing route building time, reducing intersection between clusters and improving the energy efficiency etc.