The recent advancements of technology in robotics and wireless communication have enabled the low-cost and large-scale deployment of mobile sensor nodes for target tracking, which is a critical application scenario of wireless sensor networks. Due to the constraints of limited sensing range, it is of great importance to design node coordination mechanism for reliable tracking so that at least the target can always be detected with a high probability, while the total network energy cost can be reduced for longer network lifetime. In this paper, we deal with this problem considering both the unreliable wireless channel and the network energy constraint. We transfer the original problem into a dynamic coverage problem and decompose it into two subproblems. By exploiting the online estimate of target location, we first decide the locations where the mobile nodes should move into so that the reliable tracking can be guaranteed. Then, we assign different nodes to each location in order that the total energy cost in terms of moving distance can be minimized. Extensive simulations under various system settings are employed to evaluate the effectiveness of our solution.