Stable-protocol (SP) output consensus analysis and design for high-order linear time-invariant swarm systems with switching topologies are dealt with. Firstly, on the basis of observability decomposition, a dynamic output feedback consensus protocol with switching topologies is given. Then, a necessary and sufficient condition for SP output consensus is shown, and an explicit expression of the output consensus function is presented, which is independent of switching topologies. Furthermore, necessary and/or sufficient conditions for SP output consensualization, which are independent of the number of agents, are shown respectively. Finally, a numerical example is shown to demonstrate theoretical results. Copyright © 2012 John Wiley & Sons, Ltd.