Aiming at the shortcomings of single and no adjustable code rate of traditional telemetry digital signal source, an adjustable code rate telemetry PCM digital signal source based on FPGA was designed. The method uses the technology of digital frequency synthesis DDS to provide the continuously adjustable clock signal, and the code rate of signals can be adjust between 1bps～10Mbps, it can realize regulation with characteristics of speed, small step and high resolution. Experimental results showed that the signal source could output PCM digital signals, and the code rate of signals can be set though the PC software by the users.