In modern communication technology, frequency source is a very important part of communication system. This paper designs a frequency source with an output frequency of 1GHz based on Phase-locked Loop (PLL) frequency synthesis technology. First of all, it introduces the principle of PLL frequency synthesis technology. And as the important parts of this system, third-order passive RC loop filter and output matching network are presented. Later, simulation results are achieved by Advanced Design System (ADS) software. Then, the process of software design is presented. Finally, the circuit board is produced and tested. Experiment results show that the power of PLL can reach -5dBm and its phase noise is under -76dBc/Hz@1kHz at 1GHz.