Abstract: With the development of space science and technology, the contradiction between the increasing load data type and data transmission rate and the insufficient data processing and transmission capacity has become increasingly prominent. In order to solve this problem, a kind of onboard data multiplexing based on CCSDS AOS protocol is designed. The design scheme can receive real-time telemetry data, playback data through the LVDS interface, and 1553B bus data, receive engineering telemetry data and voice data through the RS422 interface. And multiplex the above data, framing, scrambling, and then downlink.