Provided is a network system and a method for determining a network path, the network system including a plurality of extension units, each containing dualized basic units and dualized extension Ethernet modules, a first ring network connected by a first basic unit and a plurality of first extension Ethernet modules, and a second ring network connected by a second basic unit and a plurality of second extension Ethernet modules, wherein the first extension Ethernet module or the second extension Ethernet module transmits or receives data along a network path determined by judging, by the first extension Ethernet module or the second extension Ethernet module, if the first ring network is connected to the second extension Ethernet module using an intrinsic number of each extension Ethernet module.