For improvement of the code rate, Multi-Symbol Detection(MSD) and Turbo Product Code(TPC) technology is applied in PCM-FM telemetry system more and more. Only by reasonably selecting the intermediate frequency bandwidth in the telemetry system can the communication quality be guaranteed. In this paper, the spectrum characteristic of MSD and TPC technology applied to PCM-FM telemetry signal is analyzed, and the best intermediate frequency bandwidth selection method in practical application is provided.