A method of generating a flow label of an Internet Protocol version 6 (IPv6) is provided. A terminal generates a flow label to have four tuple information selected from five tuple information according to the provided method when the terminal creates a header. A network device classifies flows based on the four tuple information in the flow label generated according to the provided method. Since the flow label is generated to include only selected information and the network device analyzes less amount of information to classify the flows, the processing overhead is reduced. Also, since the terminal generates the flow label with selected essential information to classify the flows, the network device can finely classify the flows. Therefore, the differentiated service can be provided.