Focusing on the limited power characteristic of wireless sensor network, a kind of energy-efficient time synchronization algorithm for wireless sensor network which combines unidirectional reference broadcast and pair-wise mechanism is proposed. In the synchronization phase, nodes in the network repeat synchronization message alternatively. Simulation test shows this algorithm decreases the number of sending packages in the synchronization phase, provides a certain synchronization precision with the precondition of energy-saving, the node’s energy in consumed averagely, it is suitable for wireless sensor network system used for all-time surveillance for certain areas or important objects.