Time synchronization is a crucial component for wireless sensor network (WSN), because large populations of sensor nodes will collaborate in order to complete the data gathering, data fusion and localization. In a wireless sensor network with large scale of energy limited nodes, multi-hop time synchronization is necessarily applied. Some protocols such as RBS and TSPN can be used based on a spanning tree network for multi-hop. However most of the methods mainly focus on the precision of synchronization. In fact energy efficiency is also a challenge in a resource-limited WSN. In this paper an improved scheme of multi-hop time synchronization is proposed with the purpose of reducing energy consumption and lengthening sensor nodes' life. Performance analyses and simulations are also presented. First the proposed method has a better synchronization error performance. Second this proposed scheme consumes less energy than RBS and can decrease overhead.