A wireless sensor network includes an aggregator, a control device, a bridge device, and a mesh module. The control device is connected with the aggregator and the bridge device. The mesh module is wirelessly connected with the bridge device and the control device. A mesh network is built by the connections of the mesh module, the bridge device, and the control device. A duty cycle of the mesh module is less than or substantially equal to 10 percent. A command sent by the aggregator is converted into a wireless message by the control device, the wireless message is transmitted by the control device and retransmitted through a first amount of radios and repeated for a second amount of times by the bridge device, so that the wireless message is successfully received by the mesh module. Therefore, a mesh network with high efficiency and low cost is achieved.