A method of assigning a core to process a packet in a data network and a device using the same are provided in the present invention. The method comprises: extracting a traffic flow identifier from a packet in a traffic flow of a link in the data plane; performing a HASH function calculation on the traffic flow identifier to generate a HASH result V; performing a logical AND calculation on the HASH result V and a preconfigured array size parameter to generate a lookup index; using the lookup index to find a worker index in a preconfigured worker array that represents one of N cores assigned to process the packet; and processing the packet by the assigned one of N cores.