In cluster-based sensor networks, part of the sensor nodes can be switched into a sleep state in order to conserve energy if their neighbors can provide the same or almost the same sensing coverage. However, as the number of nodes in the sleep state increases, coverage for the cluster is degraded. It is crucial to maintain high coverage of clusters in order to preserve performance. In this paper, we propose a coverageaware sleep scheduling (CS) algorithm to improve the coverage of each cluster. Compared with two previous schemes: the randomized scheduling (RS) scheme and the distance-based scheduling (DS) scheme, the CS algorithm maintains higher coverage, while guaranteeing the same lifetime for the cluster. The CS algorithm thus improves the overall performance of the cluster-based sensor networks.