A data center network system and a packet forwarding method thereof are provided. The data center network system includes a virtual bridge and an address resolution protocol (ARP) server. The virtual bridge intercepts an ARP request having an identification field and a destination IP address field and adds a corresponding virtual data center identification to the identification field of the ARP request and redirecting the ARP request to the ARP server. Additionally, the ARP server queries a corresponding MAC address according to an IP address recorded in the destination IP address field of the ARP request and the corresponding VDCID recorded in the identification field of the ARP request, and transmits the corresponding MAC address in response to the ARP request. Accordingly, the same private IP address can be reused in the data center network system.