The present invention discloses a method for managing and setting many network devices, and the method is applied in a network management system. The network management system includes a management server and a plurality of network devices. The management server searches a network device connected to the management server and specifies one of the network devices connected to the management server as a master network device, and then searches all network devices that can be connected to the master network device. The searched network devices are set as candidate network devices and at least one candidate network device is set as a slave network device of the master network device, such that a single IP address of the master network device can be used for managing the slave network devices, and the management server can be used for managing many network devices distributed at different places.