As an important branch of the wireless sensor networks, wireless body area network has aroused extensive attention in various fields for its portable and mobile features. However, that the nodes are difficult to recharge or replace makes the energy issues become increasingly important. To solve this problem, this paper briefly introduced the architecture and features of wireless body area network. Next, combining with the existing researches, it analyzed and summarized some energy-efficient strategies from physical level, media access control level and network level, respectively. Finally, taking account of application requirements, it put forward several future research directions.