Abstract: Frequency agile signal source is widely used in military. The frequency conversion time plays a key role in ever-changing battlefield. This paper presents a new frequency agile program and realizes a S-band Frequency agile signal source based on this program. The frequency conversion time of this circuit is shorter than 1.5 microseconds. Advanced DDS (Direct Digital Synthesizer) chip named AD9912 which is one of the Analog Device Corporation's excellent products is adopted. Fine frequency resolution, low spurs and simple control interface are advantages of this chip. The FPGA (Field Programmable Gate Array) chip named EP2C5Q208C8 which is Altera Corporation's product is used as the control part. Some relevant tests are carried out after the frequency source circuit finished. The test results show that the frequency conversion time is shorter than 1.5μs, and the best spur suppression is 69.83dBc, while the worst one is about 40dBc.