A method of Radio Access Bearer for IP Multimedia Session in UMTS Network, including: establishing an IP Multimedia Session between the User Equipment and the IP Multimedia Subsystem; mapping associated SDP parameters into authorized IP QoS parameters, abstracting media IP packet format information from the associated SDP parameters, and transferring, said authorized IP QoS parameters and said media IP packet format information to the GPRS packet data network; mapping said authorized IP QoS parameters into authorized UMTS QoS parameters, and transforming the media IP packet format information into associated messages of RANAP; mapping media characteristics and application demands into UMTS QoS parameters by the User Equipment, and sending them to the GPRS packet data network, to compare the UMTS QoS parameters from the User Equipment with said authorized UMTS QoS parameters, and approving the PDP Context activation or update based on the comparison result by the UMTS Radio Access Network. The method according to the present invention causes the method for implementing Unequal Error Protection to be compliant with the UMTS end-to-end IP QoS structure by using the exiting SBLP-based QoS control mechanism in IMS domain, without modifying the framework of the exiting 3GPP protocol.