Wireless mesh sensor network (WMSN) is a new architecture that merges advantages of wireless mesh networks and wireless sensor networks, especially on scalability, robustness and balanced energy dissipation. Secure routing in WMSNs faces with more challenges than that in traditional sensor networks by reason of multiple sink nodes and the mobility of nodes. In this paper, we propose a scalable architecture of WMSNs, discuss and analyze key research issues under the proposed architecture, and then design two routing protocols aiming at minimizing the number of hops between a source node and a destination node and maximizing the lifetime of sensor networks. Considering new challenges to security in WMSNs, this paper also presents a secure routing protocol SecMLR, which can resist most of attacks against routing in WMSNs and work in energy-efficient way.