Based on the overall introduction of the Voice Quality System in 3G core network, this paper proposes the detailed design scheme of media information processing, including the decoding analysis of RTP protocol and the generation of CDR files. The principle and algorithm of CDR synthesis are introduced and a hash dynamic synthesis method is adopted to improve the efficiency of getting CDR. After the data processing, the system accomplishes the end-to-end voice quality analysis on basis of the relevance of RTP streams and corresponding signaling processes.