SummaryThe article studies the reachable set estimation problem for large‐scale switched systems with multimodes that have mixed switching signals consisting of both dwell time switching and arbitrary switching. First, based on a novel decentralized time‐scheduled Lyapunov function method, the method of the reachable set estimation of large‐scale switched systems is developed. By means of the novel Lyapunov function especially constructed for large‐scale switched systems, a sufficient condition is derived to ensure that the systems state is constrained in the prescribed set under the mixed dwell time switching and arbitrary switching. The concept of a decentralized control synthesis is then introduced and a time‐varying decentralized state feedback controller is developed to ensure the state trajectories of closed‐loop large systems are confined in a prescribed set. Finally, some examples are provided to illustrate our results.