A method of service level differentiation at a radio access network, a wireless network system and a radio access network (RAN) access node are provided. The method of service level traffic differentiation at the radio access network includes the following steps: A core network transmits a data flow information including a flow ID to a RAN access node via a user plane packet of an interface between the core network and the RAN access node. The RAN access node sets up a data connection with a user equipment according to the data flow information.