A server cluster including a network switch and multiple server nodes is provided. The network switch is connected to an external network. Each server node includes a network port, a network chip and a control unit. The network port is connected to the network switch via a cable. The network chip detects the cable to obtain a connection state with the external network at the server node after the network switch is started, and accordingly outputs a connection state signal. The control unit turns on or shuts down the server node according to the connection state signal and an on/off state of the server node.