A method for discovering a network device is disclosed for executing a discovery procedure of the network device in a Data Link Layer (i.e. Layer 2 of OSI 7 Layers Model) via a Network Management Server (NMS) within a Local Area Network (LAN) system to discover other network devices within the LAN. Firstly, sending a discovery packet from a Network Management Server (NMS), wherein the discovery packet comprises a command for requesting the network device to send back a corresponding Media Access Control (MAC) address. Then, receiving the discovery packet by at least one of the network device, and generating a response packet corresponding to the discovery packet for sending the response packet, wherein the response packet comprises the Media Access Control (MAC) address of the network device. Then, receiving the response packet from the NMS for collecting the MAC address while ignoring an IP address in the response packet, and updating a device information table according to the MAC address for identifying the network device.