Abstract: Some problems about overall design of a small unmanned air vehicle telemetry system are presented in this paper.The construction and fundamental principle of the telemetry system is simply introduced.According to the telemetry task requirement,the key problems which should be solved at first are demonstrated mainly by system's capacity design and channel design.The needed data transmission rate is carefully calculated with the telemetry parameter table provided by user and on this basis the frame structure is decided.The bit error rate in factual telemetry channel is grossly estimated in theory and a channel encoding scheme is provided to improve data transmission quality to meet with the requirement for extremely low bit error rate.