Abstract: In the modern electronic equipment complex frequency source is achieved by frequency synthesis technology. Good performance of frequency synthesis system is the engineering foundation of realizing frequency synthesis. In actual synthesizer circuit，the emergence of the influencing factors such as phase noise and spurious components is inevitable. It reduces the stability of the circuit，and the output is not ideal. If it is severe it can lead to system failure. It is necessary on the basis of the actual circuit compose the system concept map. According to the characteristics of the target signal，add test objectives and projects，optimization design the phase-locked loop frequency synthesizer circuit system. Use the ADS2011 to simulate the circuit and establish the relevant circuit model. Find out the optimal point and optimize circuit by observing related parameters based on a variety of test components. Simulation of the actual signal synthesis process，improve the stability and availability of the actual circuit.

Key words: PLL, Frequency, Synthesis , ADS , Simulation