The present invention provides a method for using Differentiated Services (DiffServ) to implement the IP packet classification and the marking of a Differential Service Code Point (DSCP) for the quality of service (QoS) in the wireless access network of the IP-based universal mobile telecommunication system (UMTS). The present invention makes a classification to the data stream which is outgoing from the Iub interface at the Node B side, data stream which is outgoing from the Iub interface at the RNC side and data stream which is outgoing from the Iur interface at the RNC side according to the direction and the process of the respective data streams, and assigns and adjusts the priority of the data stream classified according to the principles for optimizing QoS and radio resources. When the network is congested, the data stream with a high level will have a higher priority than that with a lower level in queue and source occupancy, and the packet with a lower priority in the same queue is discarded. The DiffServ only contains a limited number of service levels and has little condition information, thus easy to be achieved and expanded.