Recently, cooperative communication is becoming an attractive technology as it can greatly improve the spatial diversity without additional antennas. The previous works have studied the cluster-based cooperative routing to explore the energy efficiency. However, some nodes may use up their energies immediately while they always act as the cluster-heads. Thus, this paper studies the lifetime-optimal transmission scheduling for cluster-based cooperative routing problem in wireless networks. We formalize this problem into an integer programming. Then, this paper presents a polynomial-time algorithm, which mainly uses the improved branch-and-bound method to obtain the transmission scheduling on the clusters. The simulation results show that the proposed algorithm can prolong the network lifetimes about 29% and 84% compared with the previous cluster-based cooperative routing protocols.