An address detection system for detecting an address of a set top box is provided; the address detection system includes a first server and a second server. The first server includes a first parsing module and a storage module. The first parsing module parses a first request packet from the set top box, to obtain a media access control (MAC) address and a virtual Internet protocol address (IP) of the set top box. The storage module has a mapping table for storing the MAC address and the virtual IP address therein. The second server includes a second parsing module and an authenticating module. The second parsing module parses a second request packet from the set top box, to acquire the MAC address of the set top box. The authenticating module checks the mapping table for the virtual IP address corresponding to the MAC address, to authenticate validity of the virtual IP address. An address detection method is also provided.