Abstract: The telemetry decoding system of FY2 CDAS is used to demodulate coded telemetry signal to get information from Chinese FY2 meteorological satellite.The operators then analyze all these decoded data in order to know the working status of the satellite in detail.These decoded data are also transmitted to the SOCC.A redundant design,including active part and backup,enhances the reliability of the system.In case of the active equipment is out of order,the running of backup can be automatically switched.In this paper,the designing methods for a reliable telemetry decoding system are given,including subcarrier demodulation,frame synchronization,IRIGB time decoding,real time data analysis on computer etc.