Abstract: The specification of FY-3 meteorological satellite data transmission between FY-3 satellite and user ground stations is analyzed. It helps user stations to understand specification and performance requirements of FY-3 meteorological satellite data communications interface. FY-3 will provide three types of data transmission capabilities. When FY-3 satellite passes the receiving station, the three downlinks transmit simultaneously. The three downlinks include: real time direct downlink of HRPT (high resolution picture transmission); real time direct downlink of MPT (moderate resolution picture transmission); direct playback for delay time data link of DPT (delay picture transmission). HRPT transmission adopts L-band and QPSK modulator and data rate of 4.2 Mbps and EIRP (effective isotropic radiated power) of 41 dBm; MPT transmission adopts X-band and QPSK modulator and data rate of 18.7 Mbps and EIRP of 46 dBm; DPT transmission adopts X-band and QPSK modulator and data rate of 93 Mbps and EIRP of 46 dBm. Their channel coding adopts telemetry channel coding standard (CCSDS 101.0-b-5) and advanced orbiting systems-networks and data links architectural specification (CCSDS 701.0-B-2) (consultative committee for space data system (CCSDS) recommendations). DPT is transmitted only when satellite passes over China area and Svalbard area. FY-3 Meteorological Satellite will be launched in 2007, it will provide services for users to replace FY-1. National ground stations of FY-3 consist of Beijing ground station, Guangzhou ground station, Urumqi ground station and Svalbard ground station. They can receive HRPT, MPT and DPT data of FY-3. Other ground stations can receive only HRPT and MPT data of FY-3.The application data provided by the HRPT of FY-3 link are as follows: VIRR data, IRAS data, MWTS data, MWHS data, SBUS data, TOU data, MWRI data, SIM data, ERM data and SEM data. The application data provided by the MPT of FY-3 link only include science instrument data of MERSI. The application data provided by the DPT of FY-3 link are as follows: MERSI data, VIRR data, IRAS data, MWTS data, MWHS data, SBUS data, TOU data, MWRI data, SIM data, ERM data and SEM data. The transfer frames and Source Packet structure of data are consistent with CCSDS.An introduction to the physical layer on HRPT/MPT is given in this paper. The physical layer includes: RS encoding serial to parallel conversion convolution encoding synchronization and modulating. After ReedSolomon encoding and pre-pending the attached Sync Marker, data are divided into I channel and Q channel, then rate 3/4 convolution encoding for HRPT and 1/2 convolution encoding for MPT are applied, then data are modulated with QPSK modulation.The main principle, calculating method and analyzing method of FY-3 HRPT link budget and FY-3 MPT link budget are also given. The differences of data transmission among FY-3 and METOP and NPP/NPOESS are discussed. Primary strategy to design the user stations is given: when direct read out user stations design their ground stations, the ability of acquiring data must be considered. It is very important that direct read out users stations must acquire the HRPT data and MPT data of FY-3, AHRPT data of METOP and HRD data of NPP.