In this paper, we propose the cluster-based hierarchical time synchronization protocol(CHTS) for wireless sensor networks(WSN). To couple the network with real world tightly, we provide a networkwide time synchronization through the introduction of abstractions for cluster and hierarchy. Generally the error of time synchronization has the tendency of being accumulated as the hop count along the synchronization path increases in multi-hop wireless sensor network. Thus we cluster the randomly deployed nodes to decrease the hop count along the synchronization path. We then apply different optimal synchronization mechanisms to the cluster heads and cluster members for the sake of power efficiency through an explicit broadcast manner. We prove the performance enhancements with simulation comparisons.